Client#main is broken

[tobiajo]

Since this change:

   public Client() throws Exception {
 -    this(new YarnConfiguration());
 +    this.appMasterMainClass = ApplicationMaster.class.getName();
    }

Client#main is broken and therefore yarntf-submit too. The main method uses the empty constructor and now essentially lacks the following code:

    conf = new YarnConfiguration();
    yarnClient = YarnClient.createYarnClient();
    yarnClient.init(conf);
    yarnClient.start();
    opts = createOptions();

[tobiajo]

I don't want to revert this with a PR, since I don't know how/if the empty constructor is used by Hopsworks.