cluster/dht: Linkfiles creation with correct uid/gid

If renames are done with different uid/gid (non-owners), then we would
end up with incorrect uid/gid.

The fix is to create linkfiles, and heal the uid/gid as root:root. This
preserves our notion of creation as root:root and heal the uid/gid as
root:root in all paths. Additionally, we need to consider uid/gid from
only src_cached subvol, and not from linkfiles.

rename is also done as root:root if done on linkfile, as setattr of ownership
on linkfile is done after the rename

BUG: 884597
Change-Id: Ifaacd8dba0f39cb909761ffc8fe7e06cd44ec8de
Signed-off-by: shishir gowda <sgowda@redhat.com>
Reviewed-on: http://review.gluster.org/5025
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>