LUDOC-396 lnet: Add LNet Health Documentation

LUDOC-396 lnet: Add LNet Health Documentation

This patch adds the feature documentation for LNet Health,
implemented in LU-9120.

The patch also changes tabs to two spaces throughout the file.

Signed-off-by: Joseph Gmitter <jgmitter@whamcloud.com>
Change-Id: I50fcb2ceb7f35e7b423a817bb19087763ba9906a
Reviewed-on: https://review.whamcloud.com/33630
Tested-by: Jenkins
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>