Properly delete OS::Nova::FloatingIPAssociation

Currently when deleting a Nova FloatingIPAssociation, Heat sends
Nova the floating IP's Id, but Nova expects the actual IP address for
the removal. This leads to invalid database queries on Nova's side, so
this change makes sure that novaclient gets the IP address instead of the Id.

Change-Id: I15dbaf19d9467f5c65dddde77d4115b59e036b0f
Closes-bug: #1299827
Merge "Properly delete OS::Nova::FloatingIPAssociation"