Provide region_name to trove-client

To create DBaaS instance in correct data center, need to provide
region_name to trove-client. This change updates clients.py in
contrib and passes region_name to trove-client.
Please note that, this is minimial change to fix rackspace Trove
resource and there is a blueprint(multi-region-support) to support
multiple regions.

Partial-Bug: #1261870
Change-Id: I8092b23923629e21b0ba9e487f64ce7f5c826015
Merge "Provide region_name to trove-client"