CBQE-0:n1ql : errors can be not in json

Change-Id: I0a036878f2bcf383360863f14fc60f38b63e5242
Reviewed-on: http://review.couchbase.org/42536
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>