CBQE-1440: add test for mb_8538

Change-Id: Iea9a2c0dbdd3ddf60d28b67add961ae5f9b3adf6
Reviewed-on: http://review.couchbase.org/27391
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>