Currently the QEMU driver secretly sets the QEMU_AUDIO_DRV env variable
depending on how <graphics> are configured.
This introduces support for configuring audio backends from the <audio>
elements in the XML config.
The existing default behaviour is now only used if no <audio> element is
present.
All except the 'jack' audio driver are supported via QEMU's old env
variable config.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
