Using gpg 2.1 and long gpghome paths fails without meaningful error

[kornysietsma]

Gpg 2.1 has problems if you run your gpg-agent from a directory that is more than 108 characters long: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=847206

(we had this situation on some machines because our puppet rspec tests use a custom gpg home for testing)

Hiera-eyaml fails in this scenario with an error similar to:
Error from DataBinding 'hiera' while looking up 'foo::bar': Decryption failed on node baz.local

It's reasonable to fail in this scenario, but it'd be much nicer if there were some way to expose the underlying gpg errors, which are rather more meaningful.