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>
We have `get_cgroup_mountpoint()` in `utils_cgroup`. using this hard-coded cgroup directroy may cause problems in newer Linux whose cgroup dirs mounted to `/sys/fs/cgroup`.