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
Delete rackspace database resource

Rackspace database resource 'Rackspace::Cloud::DBInstance' is not
required anymore and 'OS::Trove::Instance' should be used instead.

Closes-Bug: #1261870
Change-Id: I875048995792aa9993febf1391039d3a82ec849d
Remove spurious tracebacks from tests

Some tests were deleting stacks in the background, thus provoking
tracebacks displayed later on during tests run. The patch waits for the
delete threads to prevent that.

Closes-Bug: #1278836
Closes-Bug: #1278937
Change-Id: I4b90eb6f90168803445039f9588a3052def6636a
Merge "Provide region_name to trove-client"
Merge "Delete rackspace database resource"
Merge "Remove spurious tracebacks from tests"