Orchestrator/taskreaper: Add unit-test for service remove with dead tasks.
Orchestrator/taskreaper: Add unit-test for service remove with dead tasks.

Signed-off-by: Anshul Pundir <b83733ec9a5dc60cc9eb3ca9cb86ec17acc0a878@docker.com>

alyyousuf7/swarmkit,alyyousuf7/swarmkit,docker/swarmkit,docker/swarmkit,dperny/swarmkit-1,dperny/swarmkit-1