cluster/distribute: Fix layout overlaps due to spread-count in selfheal path

We needed to zero out the layout range, before we re-calculate the range.
When spread-count is issued, we would end up with stale ranges in the layout.

Replaced dht_selfheal_dir_xattr with dht_fix_dir_xattr, which correctly resets
the un-used (after re-cal) layouts.

Change-Id: I1a900d15df07335f59356bd23182ccec34381ab2
BUG: 884455
Signed-off-by: shishir gowda <sgowda@redhat.com>
Reviewed-on: http://review.gluster.org/4648
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Anand Avati <avati@redhat.com>