Make floating_ip_bulk_destroy deallocate quota if not auto_assigned

The expected use case for floating_ip_bulk_destroy is to destroy
auto_assigned floating IPs, for which no quota is used so no quota
needs to be recovered.  But it can also be used to destroy other
(not auto_assigned) floating IPs, in which case the previously used
quota was not recovered.  This fixes the quota leak in that unusual
case.

Closes-Bug: #1254174

Change-Id: Ibff80d9ebac8d4422e401909033da12d9ec0b593
Merge "Make floating_ip_bulk_destroy deallocate quota if not auto_assigned"