Fix packaging of the QEMU guest agent
    
    The binary 'qemu-ga' is not a userspace emulator, it is the
    QEMU guest agent. Since this typically needs to be installed
    in the guest put it in a sub-RPM.
    
    A systemd service is used to start the agent. A udev rule is
    used to automatically start the systemd service, if the
    corresponding virtio-serial port is present