cluster/distribute: Reopen fds in migration internally as root:root

Though linkfile_create and rebalance dst file create sent a setattr
with correct ownership, there is still a race window where the linkfile
open (client open due to migration) will fail, as its ownership will be
root:root.

Change-Id: I056092da6102319efa3bb9f1795f8c97db2a3fed
BUG: 884597
Signed-off-by: shishir gowda <sgowda@redhat.com>
Reviewed-on: http://review.gluster.org/4513
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
Reviewed-by: Anand Avati <avati@redhat.com>