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>
4 files changed