Bulk API: Ensure that index specific failures do not affect whole request

Before a bulk request is executed, missing indices are being created by default.
If this fails, the whole request is failed.

This patch changes the behaviour to not fail the whole request, but rather all
requests using the index where the creation has failed.

TODO: Need someone to review if this kind of exception handling is correct, or if there are accidentally too much exceptions being ignored.
TODO: Need someone to review if never failing a bulk request in the `onFailure()` method is ok. I cant think of exceptions, but I think they might exist :-)

Closes #4987