qemu: introduce chardevStdioLogd to qemu private data

qemu: introduce chardevStdioLogd to qemu private data

In QEMU driver we can use virtlogd as stdio handler for source backend
of char devices if current QEMU is new enough and it's enabled in
qemu.conf.  We should store this information while starting a guest
because the config option may change while the guest is running.

Signed-off-by: Pavel Hrdina <phrdina@redhat.com>
Reviewed-by: John Ferlan <jferlan@redhat.com>