Add test that throws exceptions during search execution

Currently we only test if readers are correctly released when exceptions
occur during reopen or flush. This commit adds a test that
randomly throws exceptions during the search execution ie. when Terms
are pulled or if a docs enum is created.
Add @Slow annotation to bad apples
Start Test nodes sometimes without mock modules

We are mocking out some functionality to add assertions etc. or
randomize store types. We should randomly run with our defaults to make
sure we don't hide any potential problems.