Some fixes for early support for Python3.10

The loop parameter has been removed from most of asyncio‘s high-level API following deprecation in Python 3.8.

gns3server/utils/asyncio/embed_shell.py

@@ -352,7 +352,7 @@ if __name__ == '__main__':
     # Demo using telnet
     shell = Demo(welcome_message="Welcome!\n")
     server = create_telnet_shell(shell, loop=loop)
-    coro = asyncio.start_server(server.run, '127.0.0.1', 4444, loop=loop)
+    coro = asyncio.start_server(server.run, '127.0.0.1', 4444)
     s = loop.run_until_complete(coro)
     try:
         loop.run_forever()