LU-8066 misc: replace /proc with "lctl get/set_param"

LU-8066 misc: replace /proc with "lctl get/set_param"

Replace most remaining references to /proc or /sys with equivalent
"lctl get_param" or "lctl set_param" usage.  Discourage direct
use of /proc and /sys values from user scripts.

The description of l_getidentity and associated parameters was
duplicated in multiple places, differentiate the l_getidentity
documentation from the parameter interface for identity_upcall
and identity_info.  Add in descriptions of the identity_expire
and identity_acquire_expire parameters as well.

Add better descriptions of the debug masks, adding in missing
mask values.  Replace use of sysctl for setting and getting
the debug mask with lctl.

Rename a few section labels to give them human-readable names.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I69e27511563a948f2148d9d39480f83a0f67eca6
Reviewed-on: https://review.whamcloud.com/33686
Tested-by: Jenkins
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Ben Evans <bevans@cray.com>
Reviewed-by: Joseph Gmitter <jgmitter@whamcloud.com>