qemu: Refresh RTC adjustment on qemuProcessReconnect

qemu: Refresh RTC adjustment on qemuProcessReconnect

https://bugzilla.redhat.com/show_bug.cgi?id=1139766

Thing is, for some reasons you can have your domain's RTC to be
in something different than UTC. More weirdly, it's not only time
zone what you can shift it of, but an arbitrary value. So, if
domain is configured that way, libvirt will correctly put it onto
qemu cmd line and moreover track it as this offset changes during
domain's life time (e.g. because guest OS decides the best thing
to do is set new time to RTC). Anyway, they way in which this
tracking is implemented is events. But we've got a problem if
change in guest's RTC occurs and the daemon is not running. The
event is lost and we end up reporting invalid value in domain
XML. Therefore, when the daemon is starting up again and it is
reconnecting to all running domains, re-fetch their RTC so the
correct offset value can be computed.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>