Remove iptables >1.4.11 specific functionality

Scientific Linux 6 (and likely other similar distributions such as CentOS 6) ship with iptables 1.4.7, which doesn't support the -C flag.

Looking at examples of how other systems are handling this, Saltstack actually parses the help document to figure out if "--check" is present, and then either uses it (if present), or does something similar to this patch (if absent): https://github.com/saltstack/salt/blob/d50fdcb456ab69407610c5fa2abab68605af8084/salt/modules/iptables.py#L462

@thockin This is a continuation of #1979, now with ~100% more actually working, less bash, and a bit more testability.

I'm getting the same results for the e2e tests for this and master (using vagrant to run it): basic.sh and guestbook.sh passing and the others failing.

Edit: After some confusion, it looks like I'm mistaken about this requiring a kernel upgrade. I've removed that sentence.
Note: This whole function is doing roughly structural set equality. If there's a way to do set equality in golang that I'm missing, that would probably be more elegant.