ISPN-3761 Tests from org.infinispan.query.dsl.embedded package fail on a...

...ll environmets

https://issues.jboss.org/browse/ISPN-3761

I made the tests more robust. Instead of manually removing (cleaning) the index from the file system after each method, I only do it BeforeClass and AfterClass, and remove cache entries after each test method (which results in removing them from the index as well, i.e. cleaning the index for next test method). 

Also, I did not use cache.clear() because it takes too long (a few seconds) to execute it together with TestingUtil.killCacheManagers. Removing individual entries is much faster.

Tested on Win 2012 - passed.