Add the basic test case iptable

*A bacis class iptable_base for adding case in the future
*Subcase iptable_remove to check if container's iptable rules removed after stop.

Line-escapes are best avoided when possible, if it only means a few more lines.  It makes it easier for debugging also, so:

    before = set(self.sub_stuff['net_device_list'])
    after = set(self.read_veth_device())

Then for the ``failif()`` below, there's no point in printing ``net_device_list`` because it will be empty or > 1 (could be valid for some images).  I think the most basic thing to check is:

    self.failif(before == after, "No new net devices added to: %s" % after)