libvirt.tests: Support multiple devices for multifunction test.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libvirt.tests: Add testcases for single_device of multifunction.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
libvirt.tests: Add testcases for multi_devices in multifunction.

Signed-off-by: Yu Mingfei <yumingfei@cn.fujitsu.com>
Merge pull request #1154 from yumingfei/multifunction

libvirt.tests: Support multiple devices for multifunction test.