cases: fix 1.6 build breakages also updated build failure in 1.6 Bench wrapper TBR Change-Id: I46d13d5ee2083e46234f29548af6608bcc39ade4 Reviewed-on: https://go-review.googlesource.com/29181 Run-TryBot: Marcel van Lohuizen <mpvl@golang.org> Reviewed-by: Marcel van Lohuizen <mpvl@golang.org>