LU-9859 libcfs: replace memory_presure functions by standard interfaces

LU-9859 libcfs: replace memory_presure functions by standard interfaces

Use memalloc_noreclaim_save() and memalloc_noreclaim_restore(),
and for testing, just directly test the flag in current->flags

Linux-commit: fa399093620b867afe7686be47f197c8f17908c5

Change-Id: Id8f68164a7532ee4a816c71aff922f484c04877d
Signed-off-by: Mr NeilBrown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-on: https://review.whamcloud.com/38211
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>