If the REST endpoint consumes POST requests with invalid data, check that response with error message is trimmed to reasonable size.

Initial motivation for this was that when invalid data are very big and error messages are logged, server could be attacked by filling disk with logs.
See https://issues.jboss.org/browse/JBEAP-6316.

However, error messages are no longer printed to server.log - probably because of this: https://github.com/resteasy/Resteasy/pull/1485/files#diff-382f0c06d12f9f68e087b45142ad2564R17.