LU-14750 lnet: use ni fatal error when calculating net health

LU-14750 lnet: use ni fatal error when calculating net health

When ni is flagged with "fatal_error" by LND, its health score
remains unaffected. This allows for the net containing such ni
to be selected for tx even if it is the only ni in this net.
Take "fatal_error" status of the ni into account when calculating
the net health score.

Test-Parameters: trivial
Signed-off-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Change-Id: Ib76245f835f1458873f0c05ad9b6727d295857de
Reviewed-on: https://review.whamcloud.com/43962
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>