LU-11062 libcfs: use save_stack_trace for stack dump

LU-11062 libcfs: use save_stack_trace for stack dump

The stacktrace_ops has been removed recently. So we
have to use save_stack_trace_tsk for stack trace
dump.

Signed-off-by: Yang Sheng <ys@whamcloud.com>
Change-Id: Icb3d0dbd62c35fdd9b8de925aec9358a2208814f
Reviewed-on: https://review.whamcloud.com/32952
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>