geo-rep: Fix ValueError - signal only works in main thread

When a worker process not confirmed within 60 seconds of start
then monitor thread was terminated instead of stopping and restarting
the worker thread.
Before terminate monitor thread tries to add a signal handler for
SIGTERM to cleanup the stuff before terminate. Signal handling will
not work inside thread, so ValueError was raised.

This patch will not terminate monitor thread, instead only kills and
restarts the worker.

Change-Id: I14df26c0cc3097af29293c81536c13b86075e28f
BUG: 1078068
Signed-off-by: Aravinda VK <avishwan@redhat.com>
Reviewed-on: http://review.gluster.org/7294
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>