virsh: support remaining domain events
    
    Earlier, I added 'virsh event' for lifecycle events, to get the
    concept approved; this patch finishes the support for all other
    events, although the user still has to register for one event
    type at a time.  A future patch may add an --all parameter to
    make it possible to register for all events through a single
    call.
    
    * tools/virsh-domain.c (vshDomainEventWatchdogToString)
    (vshDomainEventIOErrorToString, vshGraphicsPhaseToString)
    (vshGraphicsAddressToString, vshDomainBlockJobStatusToString)
    (vshDomainEventDiskChangeToString)
    (vshDomainEventTrayChangeToString, vshEventGenericPrint)
    (vshEventRTCChangePrint, vshEventWatchdogPrint)
    (vshEventIOErrorPrint, vshEventGraphicsPrint)
    (vshEventIOErrorReasonPrint, vshEventBlockJobPrint)
    (vshEventDiskChangePrint, vshEventTrayChangePrint)
    (vshEventPMChangePrint, vshEventBalloonChangePrint)
    (vshEventDeviceRemovedPrint): New helper routines.
    (cmdEvent): Support full array of event callbacks.
    
    Signed-off-by: Eric Blake <eblake@redhat.com>