Druidry should correctly handle Druid query errors

[bbecker-te]

Druidry does not correctly deserialize exception responses from Druid. When there is a Druid error, the response will have a body like {error: “abcdefg”} while an actual Druid response will be an array []. Druidry does not properly deserialize it and throws a MismatchInputException.

We worked around this by handle 400 errors as QueryException in our overridden version of the Druidry Jersey client. That way we can get a more meaningful error description. However, this should really be part of the Druidry library.