LU-1274 osc: Do not grab mutex of cl_lock for glimpse

LU-1274 osc: Do not grab mutex of cl_lock for glimpse

Otherwise this will cause client eviction if that lock is being
flushed and OST happens to be slow to finish the IO.

Signed-off-by: Jinshan Xiong <jinshan.xiong@whamcloud.com>
Signed-off-by: Bob Glossman <bogl@whamcloud.com>
Change-Id: I4d7d9e8c275653d4e3f50f81dc416142d4905377
Reviewed-on: http://review.whamcloud.com/2808
Tested-by: Hudson
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>