cluster/afr: Fix bugs in quorum implementation

- Have common place to perform quorum fop wind check
- Check if fop succeeded in a way that matches quorum
  to avoid marking changelog in split-brain.

BUG: 1066996
Change-Id: Ibc5b80e01dc206b2abbea2d29e26f3c60ff4f204
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/7600
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Ravishankar N <ravishankar@redhat.com>