LU-16607 tests: Use real IPs for router tests

LU-16607 tests: Use real IPs for router tests

Use real IPs for some of the router tests in sanity-lnet. By this we
mean use IPs that are on the same network as the interface that is
configured for LNet. This decreases the time it takes to clean up
from some test cases because socklnd is able to tear down connections
more easily.

For example, running all of sanity-lnet in a single node config takes
approximately 912 seconds without this patch. With this patch it takes
190 seconds.

validate_gateway_nids() is also enhanced to check that each gateway
nid that is expected to be configured is present in the actual
yaml configuration.

Test-Parameters: trivial testlist=sanity-lnet
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I962c6a52c411f27ed7f0258e1840073da12f31f0
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50175
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>