Port improvements to Hibernate Search integration tests from the Hibernate Search codebase

As a follow up on ISPN-5255, unfortunately we found some needed fixes in the Hibernate Search integration tests with the Infinispan Directory in the Hibernate Search codebase, just while we were migrating it to Infinispan.

I've rejected the PR as the module is to be considered "frozen" in Hibernate Search, we should see if there is something of value to be applied to the migrated tests:

https://github.com/hibernate/hibernate-search/pull/797#issuecomment-87802467