qemu: Avoid duplicate resume events and state changes

The only place where VIR_DOMAIN_EVENT_RESUMED should be generated is the
RESUME event handler to make sure we don't generate duplicate events or
state changes. In the worse case the duplicity can revert or cover
changes done by other event handlers.

For example, after QEMU sent RESUME, BLOCK_IO_ERROR, and STOP events
we could happily mark the domain as running and report
VIR_DOMAIN_EVENT_RESUMED to registered clients.

https://bugzilla.redhat.com/show_bug.cgi?id=1612943

Signed-off-by: Jiri Denemark <jdenemar@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>