Use fully qualified hostname as default to advertise brokers

[merlimat]

Motivation

There is a difference in getting hostnames between Java 8 and Java 11.

In Java 8 InetAddress.getLocalHost().getHostName() was returning the fully qualified hostname while in 11 is returning the simple hostname. We should rather use the getCanonicalHostName() which is return the fully qualified hostname.
This is the same method to get the advertised address for bookies as well.

Example:

import java.net.InetAddress;
public class test{
  public static void main(String[] args) throws Exception {
    System.out.println("Hostname: " + InetAddress.getLocalHost().getHostName());
    System.out.println("Canonical Hostname: " + InetAddress.getLocalHost().getCanonicalHostName());
  }
}

# Java 8
$ java test
Hostname: broker-0.broker.pulsar.svc.cluster.local
Canonical Hostname: broker-0.broker.pulsar.svc.cluster.local

# Java 11
$ java test
Hostname: broker-0
Canonical Hostname: broker-0.broker.pulsar.svc.cluster.local