Adding the test case test_active_standby_failover under lbaas
1. In a lbaas active-standby verify traffic flows through only Active
2. Bring the Active down and verify if the failover happens and the traffic
   flows through standby.
Merge pull request #154 from stnaik/stnaik_lbaas_test

Adding the test case test_active_standby_failover under lbaas