LU-2285 osp: Block new reservations during orphan recoveries

LU-2285 osp: Block new reservations during orphan recoveries

If a thread reserves a pre-created object during an orphan recovery,
it may get an orphan that is being destroyed by the orphan cleanup
request.  This patch introduces a new flag, opd_pre_recovering, to
indicate an OSP is doing orphan recovery and makes sure new
reservations are blocked at least until the orphan recovery is done.

Change-Id: If011de57d0e365768ea28a705c864388eaed76d4
Signed-off-by: Li Wei <wei.g.li@intel.com>
Reviewed-on: http://review.whamcloud.com/4590
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>