libvirt.test: Add abnormal resource test for some commands

These testcases test if commands executed succeed when
resource becomes to abnormal, like lack disk, cpu disable.

Signed-off-by: Li Yang <liyang.fnst@cn.fujitsu.com>
Actually, it's just a directory, no matter what name it is(even '/test' is fine, '/test/cpuset' will be create for cpuset controller in test). and `get_cgroup_mountpoint()` is just get controller's current directory, not what I want.