Use hostname for bookie rackawareness mapping (apache#7361)

### Motivation

In apache#5607 the `useHostName()` was added with `return false`. That means that the rackaware policy will try to resolve the Bookies hostname into an IP and then use that IP to figure out which rack the bookie belongs.

There are 2 problems: 
 1. The IP won't match the hostname which is recorded in the `/bookies` z-node
 2. If there is an error in resolving the bookie hostname (eg: transient DNS error), an NPE exception will be triggered and the BK client will never realize that this bookie was ever seen as available in the cluster.

```
java.lang.NullPointerException: null
	at org.apache.bookkeeper.net.NetUtils.resolveNetworkLocation(NetUtils.java:77) ~[org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.TopologyAwareEnsemblePlacementPolicy.resolveNetworkLocation(TopologyAwareEnsemblePlacementPolicy.java:779) ~[org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.TopologyAwareEnsemblePlacementPolicy.createBookieNode(TopologyAwareEnsemblePlacementPolicy.java:775) ~[org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.TopologyAwareEnsemblePlacementPolicy.handleBookiesThatJoined(TopologyAwareEnsemblePlacementPolicy.java:707) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.RackawareEnsemblePlacementPolicyImpl.handleBookiesThatJoined(RackawareEnsemblePlacementPolicyImpl.java:79) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.RackawareEnsemblePlacementPolicy.handleBookiesThatJoined(RackawareEnsemblePlacementPolicy.java:246) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.TopologyAwareEnsemblePlacementPolicy.onClusterChanged(TopologyAwareEnsemblePlacementPolicy.java:654) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.RackawareEnsemblePlacementPolicyImpl.onClusterChanged(RackawareEnsemblePlacementPolicyImpl.java:79) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.RackawareEnsemblePlacementPolicy.onClusterChanged(RackawareEnsemblePlacementPolicy.java:89) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.BookieWatcherImpl.processReadOnlyBookiesChanged(BookieWatcherImpl.java:190) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.client.BookieWatcherImpl.lambda$initialBlockingBookieRead$2(BookieWatcherImpl.java:209) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.discover.ZKRegistrationClient$WatchTask.accept(ZKRegistrationClient.java:139) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
	at org.apache.bookkeeper.discover.ZKRegistrationClient$WatchTask.accept(ZKRegistrationClient.java:62) [org.apache.bookkeeper-bookkeeper-server-4.10.0.jar:4.10.0]
```

The exception is thrown at 77, since `getAddress()` yealds a `null` given that the address is unresolved. 

```java
74        if (dnsResolver.useHostName()) {
75            names.add(addr.getHostName());
76        } else {
77            names.add(addr.getAddress().getHostAddress());
78        }
```

The default implementation for the `DnsResolver.useHostName()` is to return true.

pulsar-zookeeper-utils/src/main/java/org/apache/pulsar/zookeeper/ZkBookieRackAffinityMapping.java

@@ -214,11 +214,6 @@ public void reloadCachedMappings() {
         // no-op
     }
 
-    @Override
-    public boolean useHostName() {
-        return false;
-    }
-
     @Override
     public void onUpdate(String path, BookiesRackConfiguration data, Stat stat) {
         if (rackawarePolicy != null) {