nixos/tests/knot: wait for successful zone transfers

Depending on the startup order of the two machines it might take a few
moments to get both zones transfered, which can lead to SERVFAIL
responses on busy machines.

Changed files
+4
nixos
tests
+4
nixos/tests/knot.nix
···
primary.wait_for_unit("knot.service")
secondary.wait_for_unit("knot.service")
+
for zone in ("example.com.", "sub.example.com."):
+
secondary.wait_until_succeeds(
+
f"knotc zone-status {zone} | grep -q 'serial: 2019031302'"
+
)
def test(host, query_type, query, pattern):
out = client.succeed(f"khost -t {query_type} {query} {host}").strip()