rdbms: fix finalization stage errors in LBFactory::commitMasterChanges

rdbms: fix finalization stage errors in LBFactory::commitMasterChanges

If a pre-commit callback caused a new LoadBalancer object to be created,
that object will be in the "cursory" state rather than the "finalized"
state. If any callbacks run on an LB instance, make LBFactory iterate
over them all again to finalize these new instances.

Make LoadBalancer::finializeMasterChanges allow calls to
already-finalized instances for simplicity.

Bug: T193668
Change-Id: I4493e9571625a350c0a102219081ce090967a4ac