Architecture thoughts

There should be a single entry point for authentication. We should use something like os_client_config to manage credentials and create clients.
Can we separate export/import actions? E.g., first export data from source cloud environment into a directory:
```
  os-migrate --cloud src_cloud --datadir mydatadir export
```
And then import that data into the target cloud:
```
  os-migrate --cloud dest_cloud --datadir mydatadir import
```
The advantage to this model is that it does not require the ability to connect to both environments from the same location. Actually moving data around this way (volumes, images) might be tricky. Maybe we just export the metadata and a separate command takes care of actual data movement?
Can we used a plugin model for what we export/import? E.g., use something like stevedore to look up available datasource drivers.

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