LU-1129 obdfilter: handle race condition of recreating objects

LU-1129 obdfilter: handle race condition of recreating objects

During OST recovery, a race can happen while handling replayed
OST_WRITE request during the MDS->OST orphan recovery period to
recreate missing objects, which can trigger ASSERTION(diff >= 0)
failure.

This patch handles the above issue by adding obd->obd_recovering
into the assertion to check whether the OST is in recovery or not.
If it's in recovery and diff < 0, then no assertion failure occurs,
the object has been recreated. If the OST is not in recovery and
diff < 0, then the assertion failure occurs.

Test-Parameters: envdefinitions=SLOW=yes,ENABLE_QUOTA=yes testlist=sanity-quota
Signed-off-by: Jian Yu <jian.yu@intel.com>
Change-Id: I346875378802385a95b0832b76d19f9957910cdf
Reviewed-on: http://review.whamcloud.com/5013
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Johann Lombardi <johann.lombardi@intel.com>