parallels: handle events from parallels server
    
    Subscribe to events from parallels server. It's
    needed for 2 things: to update cached domains list
    and to send corresponding libvirt events.
    
    Parallels server sends a lot of different events, in
    this patch we handle only some of them. In the future
    we can handle for example, changes in a host network
    configuration or devices states.
    
    Signed-off-by: Dmitry Guryanov <dguryanov@parallels.com>