Fix failed to delete the NovaFloatingIPAssociation resource

Unable to delete a CREATE_FAILED stack which the NovaFloatingIPAssociation
resource create failed. So we should check if the resource is not created
successful, don't try to delete it.

Change-Id: I0eba68cc2d84b2c683e66c971534afe55d391949
Closes-bug: #1318869
Merge "Fix failed to delete the NovaFloatingIPAssociation resource"