Fail geohash_cell filter if geohash prefix is not enabled
closes #4335
Override DefaultExceptionHandler to filter out certain exceptions

We have the situation that some tests fail since they don't handle
EsRejectedExecutionException which gets thrown when a node shuts
down. That is ok to ignore this exception and not fail.
We also suffer from OOMs that can't create native threads but don't
get threaddumps for those failures. This patch prints the thread
stacks once we catch a OOM which can' create native threads.