Some suggestions for better IPv6 support

[dopheide-esnet]

When specifying addresses in the [instances] section of a config there were two issues:

[instances]
agent-zeek-test-cluster1.es.net = 127.0.0.1:2151
agent-zeek-test-cluster2.es.net = 2001:400:211::122:2151

1. Previously there was no support for specifying an ipv6 address at all. This should allow the above to work as well as if the v6 address is inside []'s.

2. There's a sort in brokertypes.py that ended up trying to compare IPv4 vs IPv6 addresses causing 'ipaddress' to throw a TypeError. What I've implement here is just a basic assumption that IPv4 is less than IPv6.

[ckreibich]

Thanks Dop — I hadn't gone near IPv6 at all so it's great that you found this. It's also a good reminder that IPv6 should be in the external testsuite.

We should have a few IP address tests in test_config_io.py to cover the parsing of configs with addresses. They could work like this one, just with spelled-out IPv4/v6 addresses for instances.

It would also be good to have a test that spells out an instance's host and port, but doesn't use an IP address. I think it's currently not spelled out anywhere, but due to the underlying handling the host value needs to be an address, not a hostname. (This needn't be in this PR. It's also hopefully temporary, since eventually the framework should support hostnames and addresses throughout.)

The other day we merged #32, which means you need to rebase this one and likely tweak formatting a bit.

Let me know if you have cycles for these, otherwise I'm happy to cherry-pick your commits and take over.

[dopheide-esnet]

Okay, we should have checking for valid IPs and tests for those now. As you mentioned, I did not implement accepting hostnames yet until the underlying code does as well.

[ckreibich]

This looks great Dop, thank you. Are you up for rebasing on top of master? It's a bit fiddly due to the reformat, but otherwise not bad. Otherwise I can copy the commits from your branch and do it.

[dopheide-esnet]

I'll be honest... I have no idea how to do that. :)

This looks great Dop, thank you. Are you up for rebasing on top of master? It's a bit fiddly due to the reformat, but otherwise not bad. Otherwise I can copy the commits from your branch and do it.

[bbannier]

This got renamed to parse_from_string recently.

Here and below.