Remove unused beaconServiceFiber from C5DB, since BeaconService now handles its own Fiber creation
Rename FiberSupplier#getFiber to getNewFiber to emphasize that the returned Fiber has not been started yet
Workaround for #300 - change ReplicatedTablet so it gets its UserTabletLeaderBehavior by dependency injection, via an interface that can be mocked, so that a simple jmock expectation can be formulated, so that ReplicatedTabletTest always passes. This only partially resolves that issue because it is still not deterministic whether or not the behavior runs during the test.