LU-2179 osc: truncate partial page correctly

LU-2179 osc: truncate partial page correctly

Debug patch for osc_extent_wait() is not good because it will hit
LBUG in case the OST is in recovery. In the new patch, it will wait
again after printing an error message.

Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Change-Id: I53b5d8e335b1d4a4e57abf2964c10d7cb1ef7783
Reviewed-on: http://review.whamcloud.com/4311
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>