LUDOC-338 proc: use lctl {get,set}_param

LUDOC-338 proc: use lctl {get,set}_param

Document the use of "lctl {get,set}_param" instead of "cat" for
accessing /proc tunables and stats, since these may have been
moved to /sys or /sys/kernel/debug in newer kernels, and scripts
using "cat" will break.

Fix some places where "mdt" should be used instead of "mds" since 2.x.

Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Change-Id: I3c97d18f5397a38ff01b431cf765b3b40d8bea4b
Reviewed-on: http://review.whamcloud.com/21730
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>