cluster/dht: Do migration inprog/complete check only if ENOENT

Additionally, update op_errno to the lasted failure. If failures
found in complete_check, error returned would be EUCLEAN instead
of the right failure (in this case ENOENT)

Change-Id: Ib813867f4b817af651627b9ea07b0b09fa2b26ce
BUG: 966852
Original-author: shishir gowda <sgowda@redhat.com>
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/6495
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>