Poor error message when using same database for designate and the pool manager cache

To reproduce: In designate.conf, use the same database for designate and the pool_manager_cache. For example:

    [storage:sqlalchemy]
    connection = mysql://root:password@127.0.0.1/designate?charset=utf8
    ...

 [pool_manager_cache:sqlalchemy]
    connection = mysql://root:password@127.0.0.1/designate?charset=utf8
    ...

Then do the following:
1. Drop and recreate the designate database, if it exists
2. In either order, sync designate's database and then sync the pool_manager_cache:

    designate-manage database sync
    designate-manage pool-manager-cache sync

You should get an error message "DbMigrationError: The database is not under version control, but has tables. Please stamp the current version of the schema manually." For example: http://paste.openstack.org/show/182052/.

Expected: Designate should check for this and provide a better error message.

Note: I was running commit 889961f938519c02641ee2de27ce9cbb01348392.