add test for creating a floating IP specifying an non-existent pool

fix bug 1144353

In the bug description, the tests for Creating a floating IP specifying
the default pool and listing existing floating IPs (with an user
authorized by policy.json) have been implemented in other tests.

Change-Id: Ic77fbc2d508eeff23ca0d757ebe8d806fe06be86
3 files changed