CBQE-8260:api tests for read-only user

Change-Id: I15fa013881ec72716aa6a2546c672343767288da
Reviewed-on: http://review.couchbase.org/28112
Tested-by: buildbot <build@couchbase.com>
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>