LU-3843 clio: add debug message in osc_completion()

LU-3843 clio: add debug message in osc_completion()

Replace LASSERT with LASSERTF in osc_completion, thus we can get
more info when the LASSERT is triggered.

Signed-off-by: Niu Yawei <yawei.niu@intel.com>
Change-Id: I1b365050d5c2348b4cdc83f2ea71f36cce7f9456
Reviewed-on: http://review.whamcloud.com/7494
Reviewed-by: Bobi Jam <bobijam@gmail.com>
Tested-by: Jenkins
Reviewed-by: Jinshan Xiong <jinshan.xiong@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>