subtests...help: Fix empty list bug

Signed-off-by: Chris Evich <cevich@redhat.com>
Update case iptable

* Replace os.popen with utils.run.
* Decorating few function with staticmethod.
* Code format improved.
* Few typo issue fixed.
* Update doc that indicates outside command should work well.

Signed-off-by: Time Su <lsu@redhat.com>
Fix few typo issues and adjust code format

*Add a short sleep in case run too fast to add iptable rule

Signed-off-by: Time Su <lsu@redhat.com>