LUDOC-75 lnet: Add lst utility environment variable LST_FEATURES

LUDOC-75 lnet: Add lst utility environment variable LST_FEATURES

Change LU-521 added a new environment variable LST_FEATURES.
This change is to document LST_FEATURES in the manul.

Signed-off-by: Doug Oucharek <doug.s.oucharek@intel.com>
Change-Id: I8760bb902b45d82203645f26c0d1df3e17b8891b
Reviewed-on: http://review.whamcloud.com/3893
Tested-by: Hudson
Reviewed-by: Richard Henwood <Richard.Henwood@intel.com>
Reviewed-by: Liang Zhen <liang@whamcloud.com>
Reviewed-by: Cliff White <cliffw@whamcloud.com>