Mongo dump and restore ns translation

[bomoko]

When dumping and restoring between environments, we're need some mechanism to allow us to identify the source and target databases, using the nsFrom option during restore.

This complicates things somewhat as we need to now transfer DB name information between source and target (something we don't have to do with other sync types).

We could:

1. Make use of prerequisite gathering to get the various DB names
2. Ask the user to provide the source and destination DB names
3. Have the DB name somehow parceled as part of the transferresource