Flaky tests due to ZK client name resolution delays

ndimiduk and I ran into this issue (separately) and we noticed that there are some performance issues with name resolution in the Zookeeper client. Since we use ZK heavily in the unit tests, this often manifests as the following issues

1. Test time outs starting the mini cluster (Master failed to start....)
2. InterruptedException (because the tests timeout)
3. Flaky tests because a subset of the cluster fails to start for whatever reason (replication tests especially because they spawn multiple clusters).
4. ConnectionLoss to znode /hbase/xyzz.. JVM pause?

I have strong feeling that this is a possible cause for many of our flaky tests in Jenkins. Luckily, it looks like the following workaround to switch to an IP address instead of hostname makes it much quicker. There are some related discussions in the ZK community (ZOOKEEPER-1666 and related jiras).

--- a/hbase-common/src/main/resources/hbase-default.xml
+++ b/hbase-common/src/main/resources/hbase-default.xml
@@ -72,7 +72,7 @@ possible configurations would overwhelm and obscure the important.
   </property>
   <property>
     <name>hbase.zookeeper.quorum</name>
-    <value>localhost</value>
+    <value>127.0.0.1</value>
     <description>Comma separated list of servers in the ZooKeeper ensemble
     (This config. should have been named hbase.zookeeper.ensemble).
     For example, "host1.mydomain.com,host2.mydomain.com,host3.mydomain.com".

Until we figure out the actual root cause and a dependency upgrade (if needed), we should consider making this hostname to IP switch for more stable builds.