Recommend consistent host identification

ACCUMULO-3216 revealed a problem with users mixing and matching host identification schemes. Users should be careful to identify hosts consistently.

We should make this recommendation in the user manual indicating a preference for DNS/hostnames over IP addresses (because it's easier to make configuration changes and is required for Kerberos-enabled Hadoop, and in general is more robust).

We could also add a one-time warning during accumulo init or when services are started if we see an IP address in the configuration rather than a hostname, just to make sure users are aware of potential pitfalls.