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: 1159209
Change-Id: I7ca2a66ff2a438435f297b7063313214c28f3d4b
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>
Reviewed-on: http://review.gluster.org/9025