Remove the agent service and old-style backend tests

The agent service has been replaced by Pools, we should remove it
now that pools has fully merged.

Additionaly, the Backend tests rely on the Agent code, and no tests
exist for Pools based backends. This will be fixed as a priority in
Kilo 2.

Change-Id: I9cf96dbe8c079792bd55a9eab7a12efb7a983552
Merge "Remove the agent service and old-style backend tests"