glusterd: Saving geo-rep session details in a more specific path

Now saving the session details in
/var/lib/glusterd/geo-replication/<mastervol>_<slaveip>_<slavevol>
repo to distinguish between two master-slave sessions where the
slavename is same across two different clusters.

Change-Id: I57c93f55cc9bd4fe2bffe579028aaf5e4335b223
BUG: 991501
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/5488
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>