Verify more information in floating ip tests

Added checks for:
 - the response from a floating ip creation contains the
   port's fixed ip address;
 - creating a floating ip specifying a fixed ip address;
 - listing all floating ip's from an admin user;
 - non-admin user only sees his floating ip's in a list operation.

partially implement bp: improve-neutron-test-coverage

Change-Id: Ie517a8b51414f9331a8c38822054c6759ac9a01c
Merge "Verify more information in floating ip tests"