test-driver.py: Fix deadlock when the log queue gets full

If a program (e.g. nixos-install) writes more than 1000 lines to
stderr during execute(), then process_serial_output() deadlocks
waiting for the queue to be processed. So use an unbounded queue
instead.

We should probably get rid of the structured log output (log.xml),
since then we don't need the log queue anymore.

nixos/lib/test-driver/test-driver.py

@@ -143,7 +143,7 @@ class Logger:
         self.logfile = os.environ.get("LOGFILE", "/dev/null")
         self.logfile_handle = codecs.open(self.logfile, "wb")
         self.xml = XMLGenerator(self.logfile_handle, encoding="utf-8")
-        self.queue: "Queue[Dict[str, str]]" = Queue(1000)
+        self.queue: "Queue[Dict[str, str]]" = Queue()
 
         self.xml.startDocument()
         self.xml.startElement("logfile", attrs={})
@@ -391,11 +391,11 @@ class Machine:
     def execute(self, command: str) -> Tuple[int, str]:
         self.connect()
 
-        out_command = "( {} ); echo '|!EOF' $?\n".format(command)
+        out_command = "( {} ); echo '|!=EOF' $?\n".format(command)
         self.shell.send(out_command.encode())
 
         output = ""
-        status_code_pattern = re.compile(r"(.*)\|\!EOF\s+(\d+)")
+        status_code_pattern = re.compile(r"(.*)\|\!=EOF\s+(\d+)")
 
         while True:
             chunk = self.shell.recv(4096).decode(errors="ignore")