LU-613 clio: Client dead-lock during binary exec

LU-613 clio: Client dead-lock during binary exec

The root cause is clio takes attr lock and i_size_sem in reverse
order.

In my patch, I find out there is no deadlock issue any more in fault
and truncate path, so it holds i_size_sem in fault path to fix this
problem.

Change-Id: I04cca9324158a34fded6651692410e29aae2e402
Signed-off-by: Jinshan Xiong <jay@whamcloud.com>
Reviewed-on: http://review.whamcloud.com/1281
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Niu Yawei <niu@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>