In restartDeadTask we check if a task is dead and attempt to cleanly stop the task before restarting
the task again. To check if the task is dead or not, one of the things we check is if the task
thread is alive or not. Even though this is a correct check, we don't need to attempt to stop the
task in this case as the task thread is already dead.
Another fix is in KafkaMirrorMakerConnectorTask to count down the latch in case we fail to acquire
the task lock.

…ck around task lock acquire

…rrorMakerConnectorTask