Improve TestBase startup by allowing subclasses to select features

It would have to have a method like this

```

  @BeforeClass
  public static void init() throws Exception {
    cConf.setBoolean(Constants.Explore.EXPLORE_ENABLED, true);
    TestBase.init();
  }
```

which isn't very clean. What do you think about changing `TestBase` to be non-static and use @Before instead of @BeforeClass?