Being able to specify our own random ports

[mathieucarbou]

A problem we have now is that we cannot easily automate it tests because our app connects at startup to a server.

And since we are using the provided spring boot testing framework, we need to be able to pass it a customized property based on what will be the server port.

All comes down to bring the ability in Galvan to let the user choose by himself the random port he wants to use for servers.

public static Cluster CLUSTER = newCluster(2)
      .in(new File("build/cluster"))
      .withPorts(9410, 9411, etc)
      .withServerJars(Arrays.asList(new File("lib/mnm-server-5.3.1.jar")))
      .withServiceFragment(RESOURCE_CONFIG)
      .build();

__ .withPorts(9410, 9411, etc)__

CC @GaryWKeim @ljacomet @chrisdennis @anthonydahanne