Associate flavor types with datastore versions

This feature provides the ability to associate flavor
types with datastore versions.The trove-mange util enables
adding/deleting this information.The trove-client has been
changed to include a new api call:
/{tenant_id}/datastores/{datastore}/versions/{version}/flavors.
This call will return all nova flavors if no entries are found
for the said datastore-version in datastore_version_metadata,
otherwise only the entries found are returned.

Change-Id: I89fc2db0078d7884b7b3fa91f5daec68c0132dfb
Implements: blueprint associate-flavors-datastores
Merge "Associate flavor types with datastore versions"