clan join: test create vm for clan join

This adds a vm create test for the `clan join` scenario where:
  - there is no local clan to write changes to
  - a machine from a remote flake needs to be built and run
  - no users and no secrets need to be or can be managed (no flake to write files to)

pkgs/clan-cli/tests/conftest.py

@@ -18,7 +18,7 @@ pytest_plugins = [
     "command",
     "ports",
     "host_group",
-    "test_flake",
+    "fixtures_flakes",
 ]