[TEST] Add a more restrictive thread leaks filter

Today all threads are allowed to leak a suite. This is tricky since
it essentially allows resource leaks by default where for instance
test private TransportClients will never get closed and consume
resources influencing other tests. It also hides threads that
are not fully under elasticsearchs control like the Lucene
TimeLimitingCollector thread. This commit restricts the threads
that can leak a suite to the threads spawned from testclusters
and fixes sevearl places that leaked threads.

Closes #7833