Revert "client/tests: don't do dup2() dance to pass file descriptor to "tools/test-cloud-meta-mock.py""

This changed the fd passing protocol making it not compatible with
systemd-socket-activate(1).

This reverts commit 342ee618c7.

src/tests/client/test-client.py

@@ -2162,14 +2162,18 @@ class TestNmCloudSetup(TestNmClient):
             # hallucinogenic substances.
             s.listen(5)
 
+            def pass_socket():
+                os.dup2(s.fileno(), 3)
+
             service_path = PathConfiguration.test_cloud_meta_mock_path()
             env = os.environ.copy()
-            env["LISTEN_FD"] = str(s.fileno())
+            env["LISTEN_FDS"] = "1"
             p = subprocess.Popen(
                 [sys.executable, service_path],
                 stdin=subprocess.PIPE,
                 env=env,
                 pass_fds=(s.fileno(),),
+                preexec_fn=pass_socket,
             )
 
             self.md_url = "http://%s:%d" % s.getsockname()

tools/test-cloud-meta-mock.py

@@ -68,9 +68,11 @@ class SocketHTTPServer(HTTPServer):
 
 
 # See sd_listen_fds(3)
-fileno = os.getenv("LISTEN_FD")
+fileno = os.getenv("LISTEN_FDS")
 if fileno is not None:
-    s = socket.socket(fileno=int(fileno))
+    if fileno != "1":
+        raise Exception("Bad LISTEN_FDS")
+    s = socket.socket(fileno=3)
 else:
     addr = ("localhost", 0)
     s = socket.socket()