Dhcpd changes

This adds support for omapi-key and dhcpd named groups, as well as option arrays.  Here is an example of a config with these features:

```
key staging-key {
    algorithm hmac-md5;
    secret "secret==";
}

omapi-key staging-key;
option test.test code 119 = { string, string, string };

# DHCP_GROUP: Atlanta
group Atlanta {

}
```

I have many more things in my dhcpd.conf file that don't work with augeas, so I'm going to be slowly going through and probably will have a few more patches over the next few days or weeks.  The DHCP server config I'm testing is from V3.0.6 so it should be supported, but it's a very complicated config which uses things most people don't know about (it's from an ISP that was doing DOCSIS and IPTV, IP phones and various other things with the config)