Added documentation for trove-manage

No documentation was being generated for the trove-manage CLI of the
database project. Since *-manage CLIs are now supported by the
openstack-auto-commands tool, this has been added to the CLI
reference manual.

A current version of the trove-manage .xml file is included.

Change-Id: Ib8457a3c93b8c9acda8225c5795dc626485d64c4
Closes-Bug: #1338798
Merge "Added documentation for trove-manage"