CBQE-2044: tuq: add tests for concatenation

Change-Id: Ifae576ab2d728193e5224eddb0f8eb4f09a0e806
Reviewed-on: http://review.couchbase.org/33699
Reviewed-by: Iryna Mironava <irynamironava@yandex.ru>
Tested-by: Iryna Mironava <irynamironava@yandex.ru>