Added new commands for trove-manage
Added new commands for trove-manage

Two new commands are now available for the trove-manage utility.
They are:

datastore_version_flavor_add
datastore_version_flavor_delete

These were added to the clients.yaml file so they're processed properly
when generating the CLI reference documentation.

Change-Id: Ibaff3c14485dec2d31e46f494e6acaf380dc7150

openstack/openstack-doc-tools,openstack/openstack-doc-tools