Verify more information in floating ip tests(part2)

Add checks for:

- creating/updating a floating ip with an internal port with
  multiple ip addresses, specifying the one that must be
  associated with the floating ip;

partially implement bp: improve-neutron-test-coverage

Change-Id: Ie05eb6924e908da5b89cf5434e8365dd2485b6d2
Merge "Verify more information in floating ip tests(part2)"