Running cucumber gives the error:

cannot load such file -- test/unit (LoadError)

These weren't supposed to make it into this PR

This is failing with the stacktrace:

Caused by:
LoadError: cannot load such file -- arel/visitors/bind_visitor
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
/usr/src/app/.bundle/ruby/2.5.0/gems/ibm_db-4.0.0/lib/active_record/connection_adapters/ibm_db_adapter.rb:13:in `<top (required)>'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `block in require'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:257:in `load_dependency'
/usr/src/app/.bundle/ruby/2.5.0/gems/activesupport-5.2.3/lib/active_support/dependencies.rb:291:in `require'
/usr/src/app/lib/octopus/proxy_config.rb:245:in `initialize_adapter'

The gem install does this, but the download is slow.  Watching
the wget progress is more satisfying.

Error message is:

ActiveRecord::StatementInvalid: NoMethodError: undefined method `[]' for
nil:NilClass:

  from octopus/lib/octopus/abstract_adapter.rb:23:in `octopus_shard'
  from octopus/lib/octopus/abstract_adapter.rb:12:in `instrument'
  from vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.11.1/lib/active_record/connection_adapters/abstract_adapter.rb:478:in `log'

This has shown to surface in the ibm_db and sqlserver adapters.

Error message is:

ActiveRecord::StatementInvalid: NoMethodError: undefined method `[]' for
nil:NilClass:

  from octopus/lib/octopus/abstract_adapter.rb:23:in `octopus_shard'
  from octopus/lib/octopus/abstract_adapter.rb:12:in `instrument'
  from vendor/bundle/ruby/2.3.0/gems/activerecord-4.2.11.1/lib/active_record/connection_adapters/abstract_adapter.rb:478:in `log'

This has shown to surface in the ibm_db and sqlserver adapters.

This allows the InstrumenterDecorator to properly log the shard name

Running tests individually works, but running the whole
migration_spec.rb file will recreate the issue _almost_
every time, in a random spec.

Here's the full error and stack trace:

Octopus::Migration should send the query to the correct shard
     Failure/Error:
       delegate :adapter_name, :add_transaction_record, :case_sensitive_modifier,
         :type_cast, :to_sql, :quote, :quote_column_name, :quote_table_name,
         :quote_table_name_for_assignment, :supports_migrations?, :table_alias_for,
         :table_exists?, :in_clause_length, :supports_ddl_transactions?,
         :sanitize_limit, :prefetch_primary_key?, :current_database,
         :combine_bind_parameters, :empty_insert_statement_value, :assume_migrated_upto_version,
         :schema_cache, :substitute_at, :internal_string_options_for_primary_key, :lookup_cast_type_from_column,
         :supports_advisory_locks?, :get_advisory_lock, :initialize_internal_metadata_table,
         :release_advisory_lock, :prepare_binds_for_database, :cacheable_query, :column_name_for_operation,
         :prepared_statements, :transaction_state, :create_table, to: :select_connection

     RuntimeError:
       An unexpected error occurred during retrieval of table metadata: uncaught throw :"Fetch Failure: <error message could not be retrieved>"
     # /usr/src/ruby-ibmdb/IBM_DB_Adapter/ibm_db/lib/active_record/connection_adapters/ibm_db_adapter.rb:1858:in `rescue in tables'
     # /usr/src/ruby-ibmdb/IBM_DB_Adapter/ibm_db/lib/active_record/connection_adapters/ibm_db_adapter.rb:1845:in `tables'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/connection_adapters/abstract/schema_statements.rb:55:in `table_exists?'
     # ./lib/octopus/proxy.rb:25:in `table_exists?'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/schema_migration.rb:20:in `block in table_exists?'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activesupport-5.0.7.2/lib/active_support/deprecation/reporting.rb:36:in `silence'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activesupport-5.0.7.2/lib/active_support/deprecation/instance_delegator.rb:20:in `silence'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/schema_migration.rb:20:in `table_exists?'
     # /usr/src/ruby-ibmdb/IBM_DB_Adapter/ibm_db/lib/active_record/connection_adapters/ibm_db_adapter.rb:48:in `create_table'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/connection_adapters/abstract/schema_statements.rb:1008:in `initialize_schema_migrations_table'
     # ./lib/octopus/proxy.rb:200:in `initialize_schema_migrations_table'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/migration.rb:1127:in `initialize'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/migration.rb:1017:in `new'
     # ./gemfiles/.bundle/ruby/2.5.0/gems/activerecord-5.0.7.2/lib/active_record/migration.rb:1017:in `run'
     # ./lib/octopus/migration.rb:187:in `block in run_with_octopus'
     # ./lib/octopus/proxy.rb:86:in `block (2 levels) in run_queries_on_shard'
     # ./lib/octopus/proxy.rb:345:in `using_shard'
     # ./lib/octopus/proxy.rb:85:in `block in run_queries_on_shard'
     # ./lib/octopus/proxy.rb:329:in `keeping_connection_proxy'
     # ./lib/octopus/proxy.rb:84:in `run_queries_on_shard'
     # ./lib/octopus/proxy.rb:93:in `block in send_queries_to_multiple_shards'
     # ./lib/octopus/proxy.rb:92:in `map'
     # ./lib/octopus/proxy.rb:92:in `send_queries_to_multiple_shards'
     # ./lib/octopus/migration.rb:186:in `run_with_octopus'
     # ./spec/support/octopus_helper.rb:46:in `migrate_to_version'
     # ./spec/support/octopus_helper.rb:37:in `migrating_to_version'
     # ./spec/octopus/migration_spec.rb:86:in `block (2 levels) in <top (required)>'
     # ------------------
     # --- Caused by: ---
     # UncaughtThrowError:
     #   uncaught throw :"\xA3\xC9\x8E+H\xEA\xC9\vX\x82g\x8B\xAAU\x00\x00\bY\r\x8C\xAAU\x00\x00\x1A\xD0\xC1\xE2\xCF\xE9\x1Dd0\xB3m\x8B\xAAU\x00\x00\x80T\r\x8C\xAAU\x00\x00\x01\x99\xD1o,"
     #   /usr/src/ruby-ibmdb/IBM_DB_Adapter/ibm_db/lib/active_record/connection_adapters/ibm_db_adapter.rb:1845:in `fetch_assoc'

This keeps the test suite going for most users that won't
be using the ibm_db gem

Docker dev system

Check that @config exists.  Fixes thiagopradi#413

DB2 ibm_db gem support

ibmdb/ruby-ibmdb#89

Until that issue is officially resolved by IBM, I'm using my local
fork for testing Octopus.

This is an oddball bug, deep in the DB2 C library.  Disconnecting
from the database during the Passenger fork process causes it to
hang indefinitely

Since we don't disconnect from DB2, this spec fails.

In many setups, the default master shard might be a different
database server in each environment.  A single `master_shard`
config setting doesn't fit.  This patch first checks
the shards.yml for `octopus` => Rails env => master_shard
for a setting, and still falls back to `octopus` => `master_shard`
if it doesn't exist

I cowboyed up a bit too fast on the first fix.  This moves the
per-environment master_shard selection to its own yaml key