Add test for svirt in virt-install.

Signed-off-by: yangdongsheng <yangds.fnst@cn.fujitsu.com>
Add svirt_install filter into guest-os.

svirt_install calls unattended_install to test install guest,
then we need to add a filter in guest-os to allow svirt_install
access the configurations.

Signed-off-by: Dongsheng Yang <yangds.fnst@cn.fujitsu.com>