This has shown to be flaky in the VM test, at least when running on
the aarch64 ofborg builder(s).
I assume it's some flakyness in systemd-networkd not being fully up, or
at least not up to the point that it properly replies to the _gateway
request.
This part of the test is supposed to test external (non-glibc) nss
module lookup for the host database works, which is already sufficiently
covered in the previous checks (for *.localhost). Drop these redundant
checks. We're not integration-testing networkd here.
nixosTests.systemd is quite heavy, it requires a full graphical system,
which is quite a big of a rebuild if the only thing you want to test is
whether dynamic users work.
This is now moved to an `nscd` test, which tests various NSS lookups,
making extra sure that the nscd path is tested, not the fallback path
(by hiding /etc/nsswitch.conf and /etc/hosts for getent).
nixosTests.resolv is removed. It didn't check for reverse lookups,
didn't catch nscd breaking halfway in between, and also had an
ambiguous reverse lookup - 192.0.2.1 could either reverse lookup to
host-ipv4.example.net, or host-dual.example.net.
