Only delete heat data in the DB if it exists
Only delete heat data in the DB if it exists

The undercloud upgrade script that deletes users may
not work if re-run or if other scripts clean DB data
during the upgrade.
Only delete users and database if it still exists in
the DB.

Change-Id: I36e3b33a824f3ae6d1da97ea53527c2b4519ea3c
Related-Bug: #1943440
Related-Bug: #1943330

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates