Add scenario test for load balancer

This test checks basic load balancing.

The following is the scenario outline:
  1. Create an instance
  2. SSH to the instance and start two servers
  3. Create a load balancer
  4. Send 10 requests to a floating ip associated with a VIP
     and check that they are shared between the two servers
     and that both of them get equal portions of the requests

bp lbaas-scenario-tests

Change-Id: Ia864a6f532ea58747f04658eb38535ee06a303cb
Merge "Add scenario test for load balancer"