geo-rep: Failover when a Slave node goes down

When a slave node goes down, worker in master node
can connect to different slave node and resume the operation.

Existing georep was not checking the status of slave node before
worker restart. With this patch, geo-rep worker will check the
node status using `gluster volume status` when it goes faulty.

BUG: 1151412
Change-Id: If3ab7fdcf47f5b3f3ba383c515703c5f1f9dd668
Signed-off-by: Aravinda VK <avishwan@redhat.com>
Reviewed-on: http://review.gluster.org/8921
Reviewed-by: Kotresh HR <khiremat@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Venky Shankar <vshankar@redhat.com>
Tested-by: Venky Shankar <vshankar@redhat.com>