qemu: convert monitor to use the per-VM event loop

This converts the QEMU monitor APIs to use the per-VM
event loop, which involves switching from virEvent APIs
to GMainContext / GSource APIs.

A GSocket is used as a convenient way to create a GSource
for a socket, but is not yet used for actual I/O.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

tests/qemumonitortestutils.c

@@ -1167,6 +1167,7 @@ qemuMonitorTestNew(virDomainXMLOptionPtr xmlopt,
                                       &src,
                                       true,
                                       0,
+                                      virEventThreadGetContext(test->eventThread),
                                       &qemuMonitorTestCallbacks,
                                       driver)))
         goto error;