Test fails when port 8080 is in use

Port 8080 is used by default on various web servers and applications. On any system running such a server the ZooKeeper build fails because the port is in use. It should use a dynamically assigned free port instead.

java.lang.NullPointerException
at org.apache.zookeeper.server.X509AuthFailureTest.testSecureStandaloneServerAuthNFailure(X509AuthFailureTest.java:81)