test/e2e: deduplicate some network subnets

With a high parallel node run we have much more test cases run in
parallel, as such I am seeing a lot of network subnet flakes as they
were using the same one and thus failed since there can only be one
config using it at a time.

Now hard coding this here is ugly, yes. But for now I just need to get
the flakes down in the new CI. Long term we should likely have a helper
that hands out known unused subnets for the tests.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>