libvirt.test: Add 'bridge' type interface test for iface

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
libvirt.test: Add more testcases for iface test

Add some case for nonexist interface test, including
protocol test, stp test

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
libvirt.test: Add 'vlan' and 'bond' type test for iface

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
libvirt.test: Add attach interface to VM case and fix some problems

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
Merge pull request #156 from liyangfnst/iface_bri

libvirt.test: Add 'bridge' type interface test for iface