CBQE-1531: add scalar fn tests

Change-Id: Id415e17a282715092663167215c0e5bed3de2916
Reviewed-on: http://review.couchbase.org/29218
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>