Elastic Feature Runner should initialize its index

When using an external elastic server, sometime the test index is not initialized because it already exists (it has been created by a previous test),
this causes random test failures if the mapping is not the expected one or if there are some trailing data.

To avoid this test suite usually adds an explicit initialization:

    @Before
    public void setupIndex() throws Exception {
        esa.initIndexes(true);
    }

This should be done at the Feature Runner level.