Catching new exception while disassociating a disassociated floating ip

Because the response of disassociating floating ip api will be
changed(bug #1129719), so the tempest codes need to be updated synchronically.

Change-Id: Ie25ed338dda01cf5e52982abae9ea85386a293a9
Merge "Catching new exception while disassociating a disassociated floating ip"