HSEARCH-1619 Using TestConstants.getIndexDirectory(Class) to determine t...

...he index directory

This is work in progress, but since @Sanne is keen to integrate, I create a first pull request. I am planning to follow up with another pull request which will try to ensure that this is problem is not happening in the future anymore. The main culprit is really _SearchTestBase#getBaseIndexDir_ which is designed to work as part of the compiled sources. It fails, if it is used bundled in the testing jar.