virt-viewer: ensure we close when seeing domain stop event
    
    Normally virt-viewer relies on the VNC/SPICE widget seeing
    an EOF on its underlying connection to detect when the
    session is closed.
    
    When tunnelling to a remote guest over SSH though, this
    EOF can be delayed for a very long time, leaving a dead
    session open.
    
    This can be seen with
    
       virt-viewer -c qemu+ssh://remotehost/system guestname
    
    when on the remote shell run
    
       virsh destroy guestname
    
    and notice that virt-viewer does not see the shutdown
    immediately.
    
    When we get a domain stopped event we know the session
    should be dead, so forceably close it, if not already
    closed.
    
    Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
    (cherry picked from commit a62827d28c6b69e90102e4c1c8043cbddad8929a)