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

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).

Lustre-change: https://review.whamcloud.com/44073
Lustre-commit: 412970c586ea189d442620316c5ed6f1fa43cc0e

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/46846
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>