Allow updates to be issued to degraded LB
Allow updates to be issued to degraded LB

An LB goes into DEGRADED status when some but not all of its members are
in ERROR.

Updates should still be allowed in a DEGRADED state lest LB policy
becomes unable to operate on any partially operational cluster.

Change-Id: If7a9d2edf8b95ce8f153777a7240b8040c4bd484

openstack/senlin,openstack/senlin,openstack/senlin,stackforge/senlin,stackforge/senlin