Cluster/DHT : Rebalance skipped file count fix

The return value in dht_migrate_file is used to indicate the status
of the file migration. This value was being masked by the lock operation
causing the skipped and failure file counts to be incorrectly calculated.

Change-Id: Ice3d2f5d57766e18aa52659f22a76867d188dc65
BUG: 1161518
Signed-off-by: Nithya Balachandran <nbalacha@redhat.com>
Reviewed-on: http://review.gluster.org/9070
Reviewed-by: susant palai <spalai@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Shyamsundar Ranganathan <srangana@redhat.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>