gsyncd: distribute the crawling load

* also consume changelog for change detection.
* Status fixes
* Use new libgfchangelog done API
* process (and sync) one changelog at a time

Change-Id: I24891615bb762e0741b1819ddfdef8802326cb16
BUG: 847839
Original Author: Csaba Henk <csaba@redhat.com>
Original Author: Aravinda VK <avishwan@redhat.com>
Original Author: Venky Shankar <vshankar@redhat.com>
Original Author: Amar Tumballi <amarts@redhat.com>
Original Author: Avra Sengupta <asengupt@redhat.com>
Signed-off-by: Avra Sengupta <asengupt@redhat.com>
Reviewed-on: http://review.gluster.org/5131
Reviewed-by: Vijay Bellur <vbellur@redhat.com>
Tested-by: Vijay Bellur <vbellur@redhat.com>