LU-8066 obdclass: move lustre server sysctl to sysfs

LU-8066 obdclass: move lustre server sysctl to sysfs

A few of the lustre sysctl are server side so lets
move those as well to sysfs. Both memused ane memused_max
are missing upstream but we need to keep them around
for now.

Signed-off-by: James Simmons <uja.ornl@yahoo.com>
Change-Id: Ie2fd2408d79aede4e40272a86f63f1e55311d1b9
Reviewed-on: https://review.whamcloud.com/24033
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: Niu Yawei <yawei.niu@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>