LU-601 mdd: Fix transaction credits

LU-601 mdd: Fix transaction credits

* mdd_create()/mdd_create_data() may need delete orphan objects on
  OSTs, so that we need preserve enough transaction credits for llog
  records.
* mdd_attr_set() may write lov llogs.
* orphan_object_destroy() also will write a llog record, we need
  reserve credit for it as well.
* add credit changelog record.

Signed-off-by: Bobi Jam <bobijam@whamcloud.com>
Change-Id: I5124d2f368e2ff794b2b2b8194bec86f63e971cf
Reviewed-on: http://review.whamcloud.com/1276
Reviewed-by: Fan Yong <yong.fan@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Mikhail Pershin <tappro@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>