LU-14790 tests: Check NI status when link is downed

Add test to check that NI status is set to down when the
ni_fatal_error_on flag is set (i.e. when a link is down).

HPE-bug-id: LUS-10167
Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: If98a899b0ee8dd9637c08774109668ad06244c60
Reviewed-on: https://review.whamcloud.com/44073
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>