Fix title of database sync Exec in mysql class

The mysql class incorrectly defined an Exec collector to match on 'heat-manage
db_sync', which is not a real Exec in the catalog. The collector silently
failed to find this resource and the notify relationship between the database and the
sync command was never created. This changes the collector to match on
heat-dbsync, which is a real exec defined in init.pp.

Change-Id: Icc8ceb25b525ba83e66c719abca31799a4d2d223