libxl: queue domain event earlier in shutdown handler

libxl: queue domain event earlier in shutdown handler

The shutdown handler may restart a domain when handling a reboot
event or when <on_*> is set to 'restart'.  Restarting consists of
calling libxlVmCleanup followed by libxlVmStart.  libxlVmStart will
emit a VIR_DOMAIN_EVENT_STARTED event, but the SHUTDOWN event is
not emitted until exiting the shutdown handler, after the STARTED
event.

This patch changes the logic a bit to queue the event at the start
of the shutdown action, ensuring it is queued before any subsequent
events that may be generated while executing the shutdown action.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>