Add clipboard support for TigerVnc

There's currently no clipboard support for servers running on TigerVnc. TigerVnc clipboard support is provided by vncconfig that needs to be spawned for every display socket. The code changes above provides that functionality

gns3server/compute/docker/docker_vm.py

@@ -86,6 +86,7 @@ class DockerVM(BaseNode):
         self._telnet_servers = []
         self._xvfb_process = None
         self._vnc_process = None
+        self._vncconfig_process = None
         self._console_resolution = console_resolution
         self._console_http_path = console_http_path
         self._console_http_port = console_http_port
@@ -615,6 +616,11 @@ class DockerVM(BaseNode):
         x11_socket = os.path.join("/tmp/.X11-unix/", "X{}".format(self._display))
         await wait_for_file_creation(x11_socket)
 
+        # Start vncconfig for tigervnc clipboard support, connection available only after socket creation.
+        tigervncconfig_path = shutil.which("vncconfig")
+        if tigervnc_path and tigervncconfig_path:
+	        self._vncconfig_process = await asyncio.create_subprocess_exec(tigervncconfig_path, "-display", ":{}".format(self._display), "-nowin")
+
         # sometimes the VNC process can crash
         monitor_process(self._vnc_process, self._vnc_callback)
 
@@ -825,6 +831,12 @@ class DockerVM(BaseNode):
                 await self.stop()
 
             if self.console_type == "vnc":
+                if self._vncconfig_process:
+                    try:
+                        self._vncconfig_process.terminate()
+                        await self._vncconfig_process.wait()
+                    except ProcessLookupError:
+                        pass
                 if self._vnc_process:
                     try:
                         self._vnc_process.terminate()