cluster/afr: Avoid order mismatch in blocking entrylks

Problem:
When taking blocking entrylks, afr orders the entrylks based on
uuid_compare of gfids of parent dirs, if they are equal then it orders
them based on the basenames. While this approach works fine, the
implementation assumes loc->gfids to be populated at the time of
the comparison, but loc may have gfid in loc->inode->gfid instead
of loc->gfid which was leading to order mismatches and dead-locks.

Fix:
Implemented loc_gfid which gives gfid by checking both loc->gfid,
loc->inode->gfid. Used this for ordering the blocking entrylks.

Change-Id: I2743fcaff3d670fbeb6b8e0a496f106a3585dde1
BUG: 965987
Signed-off-by: Pranith Kumar K <pkarampu@redhat.com>
Reviewed-on: http://review.gluster.org/5063
Reviewed-by: Krishnan Parthasarathi <kparthas@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>