LU-502 don't allow to kill service threads by OOM killer.

LU-502 don't allow to kill service threads by OOM killer.

OOM can produce a many issues like requests processing counter.

Change-Id: I8d417d148b589ea6de84c5d16bc2607a59852564
Signed-off-by: Alexey Lyashkov <alexey_lyashkov@xyratex.com>
Reviewed-on: http://review.whamcloud.com/1088
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>