glusterd : Checking session created or not in case of geo-rep stop

Performing statefile check in case of geo-rep stop, so as to provide
proper error message in case session is not created.

However in case of geo-rep stop force, we allow the command to succeed
even in case that the session is not created, because the stop command
is a failsafe command to stop running geo-rep sessions on any nodes.

Change-Id: I2b6a0253de977633606c422cbbc9e37cede9a268
BUG: 989541
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/5417
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>