[user-guides] Update the trove data stores

http://git.openstack.org/cgit/openstack/trove/tree/trove/guestagent/dbaas.py

Change-Id: Ic9ea8f95fc49e1a27709bebc0807dcee7d17ead8
Closes-Bug: #1492202

doc/admin-guide-cloud/source/database.rst

@@ -162,12 +162,18 @@ data store version.
           the data store manager is identified by one of the following
           strings, depending on the database:
 
-          * mysql
-          * redis
-          * mongodb
           * cassandra
           * couchbase
+          * couchdb
+          * db2
+          * mariadb
+          * mongodb
+          * mysql
           * percona
+          * postgresql
+          * pxc
+          * redis
+          * vertica
         - ``mysql``
 
       * - glance ID