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>
In fact, I prefer TestError for it.
Because this error may be solved by changing the environment.
While for TestNAError, it should be problem that can not be solved.