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
Adds XML support to test_live_block_migration.py

Added "live_migrate_server" method to servers_client.py
of XMl interface and XML interface Support functionality to
test_live_block_migration.py, so as to run the testscript
using both JSON and XML interfaces.

Change-Id: I75098d59fa93a6f0ca83cdeb6cb2b0620beefe73
Implements: blueprint add-xml-support
Merge "Adds XML support to test_live_block_migration.py"
Merge "add test for creating a floating IP specifying an non-existent pool"