LU-4471 mdd: mdd_unlink: do trans_start after sanity check

LU-4471 mdd: mdd_unlink: do trans_start after sanity check

Currently, mdd_trans_start is called before
mdd_unlink_sanity_check. This means a remote directory
which has files in it can be removed on MDT0 before the
sanity check on MDT1 finds the files and errors, which
orphans the files on MDT1. This patch moves the sanity
check before mdd_trans_create and mdd_trans_start.

Lustre-commit: 754a8ac8bf4b907bb579fe441eed1ba3447d3e0f
Lustre-change: http://review.whamcloud.com/8827

Signed-off-by: Patrick Farrell <paf@cray.com>
Signed-off-by: Bob Glossman <bob.glossman@intel.com>
Change-Id: Iac3cb214f16cb8e342be6691013d1cf262775ff0
Reviewed-on: http://review.whamcloud.com/9379
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>