Fix get_available_port

[sharpener6]

For both zmq and ymq, if user didn't specify the port, then port should be 0, and we should let OS to bind with available port, then return it

current behavior is we use get_available_tcp_port, then use this port to actually listen:

def get_available_tcp_port(hostname: str = "127.0.0.1") -> int:
    with socket.socket(socket.AddressFamily.AF_INET, socket.SocketKind.SOCK_STREAM) as sock:
        sock.bind((hostname, 0))
        return sock.getsockname()[1]

But there is a gap between we get_available_tcp_port and then use it, in this gap, other program might use the port, and it's not consistent. we should bind it when create zmq/ymq connection and return the port number

[gxuu]

NOTE: YMQ doesn't expose the bind operation to the user except when the socket is of type Binder which you have to provide address to before scheduler starts as the OSS needs it in some cases.

[rafa-be]

YMQ-libuv will support binding on 0, and will return the bounded port. Still need quite a little bit of refactoring on Scaler's side to broadcast the port.