Gnocchi was providing its URL to client charms before its VIP was
completely setup. This change checks that an hacluster relation
exists and if so waits to provide its URL until the hacluster setup
is complete.
Depends-On: I23eb5e70537a62d5b9e5e24d09f37519b63a1717
Change-Id: I3a6991ecb4eca8659c08d5c5d00d35b8d22bf79e
Closes-Bug: #1749280