The following changes are made to clustering datastore tests:

The following changes are made to clustering datastore tests:
 - "BuyCar" now raises an exception instead of returning True/False. Robot
   framework does not fail test on returning False. Exceptions are the
   correct way to return failure. This fixes the issue where routed RPC
   registrations hadn't been "gossiped" yet to follower1, and testcase
   did not retry because "BuyCar" hadn't failed with exception. The testcase
   is "Purchase cars on Follower1" in 010_crud_on_leader.robot. The change
   is in CrudLibrary.py.

 - "Get Leader" and "Get All Followers" now ignore any down controllers.
   The controller to ignore is passed in as an argument. Before this fix,
   "getClusterRoles" would repeatedly try to read from the downed node,
   which would cause unnecssary delays. With this fix the test cases have
   speeded up considerably. The change is in ClusterKeywords.txt,
   030_car_failover_crud_on_new_leader.robot, and
   040_people_failover_crud_on_new_leader.robot

 - Fixed a path issue in 010_crud_on_leader.robot. I would see warnings from
   robot for missing RequestsLibrary.

Change-Id: Ia72e164d667121edb3aced2f8ec6bc1c504afe5a
Signed-off-by: Shaleen Saxena <ssaxena@brocade.com>