[lldb/test] Make it possible to run the mock gdb server on a single thread

[labath]

Summary

This is a preparatory commit to enable mocking of qemu startup. That
will involve running the mock server in a separate process, so there's
no need for multithreading.

Initialization is moved from the start function into the constructor
(which can then take an actual socket instead of a class), and the run
method is made public.

Depends on D114156.

[mgorny]

I think I may have delayed constructing socket until start() for some reason but maybe it was just originally like that and didn't want to change semantics. If it doesn't break tests, wfm.

lldb/packages/Python/lldbsuite/test/gdbclientutils.py

class MockGDBServer:
 
     responder = None
     _socket = None
     _thread = None
     _receivedData = None
     _receivedDataOffset = None
     _shouldSendAck = True
 
-    def __init__(self, socket_class):
-        self._socket_class = socket_class
+    def __init__(self, socket):
+        self._socket = socket
         self.responder = MockGDBServerResponder()
 
     def start(self):
-        self._socket = self._socket_class()
         # Start a thread that waits for a client connection.
-        self._thread = threading.Thread(target=self._run)
+        self._thread = threading.Thread(target=self.run)
         self._thread.start()
 
     def stop(self):
-        self._socket.close_server()
         self._thread.join()
         self._thread = None
 
     def get_connect_address(self):
         return self._socket.get_connect_address()
 
     def get_connect_url(self):
         return self._socket.get_connect_url()
 
-    def _run(self):
+    def run(self):
         # For testing purposes, we only need to worry about one client
         # connecting just one time.
         try:
             self._socket.accept()
         except:
             return
         self._shouldSendAck = True
         self._receivedData = ""

lldb/packages/Python/lldbsuite/test/lldbgdbclient.py

class GDBRemoteTestBase(TestBase):
     """
 
     NO_DEBUG_INFO_TESTCASE = True
     server = None
     server_socket_class = TCPServerSocket
 
     def setUp(self):
         TestBase.setUp(self)
-        self.server = MockGDBServer(socket_class=self.server_socket_class)
+        self.server = MockGDBServer(self.server_socket_class())
         self.server.start()
 
     def tearDown(self):
         # TestBase.tearDown will kill the process, but we need to kill it early
         # so its client connection closes and we can stop the server before
         # finally calling the base tearDown.
         if self.process() is not None:
             self.process().Kill()