LU-2332 osc: solve a race in client obd list lock

In __client_obd_list_lock(), the lock may have been released before
printing the debug information.

Also, avoid calling osc_wake_cache_waiters() recrusively in
__osc_unreserve_grant().

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I4ada1f02feb56b7b25f2f87384551cee7265679e
Reviewed-on: http://review.whamcloud.com/4587
Reviewed-by: Prakash Surya <surya1@llnl.gov>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>