LU-16307 tests: fix sanity-sec test_31

LU-16307 tests: fix sanity-sec test_31

In order to improve sanity-sec test_31 resiliency, reorganize the way
the new LNet '999' is handled, and make sure everything is correctly
cleaned up after the test.

The test is also updated to handle IPv6 and numeric NIDs, and it has
been tweaked to run out of tree.

Test-Parameters: trivial
Test-Parameters: testgroup=review-dne-part-2
Signed-off-by: Sebastien Buisson <sbuisson@ddn.com>
Change-Id: Idd657c7555e598d0ebc08387eac537b1c73e35bd
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53818
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>