Support set deadline for qmp socket connection

[MaJin1996]

If some other process(e.g. libvirtd) occupy the qmp socket, run command will hang.

Sometimes we use go-qemu to take over VM when libvirtd stopped, but libvirtd service will start automatically at an undetermined time. Deadline could prevent the impact of race condition.

example:
`

socket, err := qmp.NewSocketMonitor("unix", sockFile, timeout)

if err != nil {
	return nil, err
}

if err := socket.SetRWDeadline(time.Now().Add(timeout)); err != nil {
	return nil, err
}

if err := socket.Connect(); err != nil {
	return nil, err
}
defer socket.Disconnect()

`