LU-13264 osc: ensure lu_ref work atomic from osc_lock_upcall()

LU-13264 osc: ensure lu_ref work atomic from osc_lock_upcall()

Since osc_lock_upcall() uses per-cpu env via
cl_env_percpu_[get,put](), all undelying work must execute on the
same CPU, meaning that no sleep()/scheduling must occur.
This implies all lu_ref related work to no longer use lu_ref_add(),
which calls might_sleep() (likely to cause a
scheduling/cpu-switch...), but lu_ref_add_atomoc() instead.

Signed-off-by: Bruno Faccini <bruno.faccini@intel.com>
Change-Id: Ide33d4c415e9e382f0bc344e2114182a1f122de6
Reviewed-on: https://review.whamcloud.com/37629
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>