all: report in standard benchmark format

This switches all benchmarks to report in the standard Go benchmark
format [1], making it possible to run and analyze these benchmarks
using tools built for standard Go benchmarks.

As part of this, we lift the repetition loop to the top level to make
it possible to report the results after each run.

[1] https://github.com/golang/proposal/blob/master/design/14313-benchmark-format.md

Change-Id: I542e0f4f6fcfa7783ee37bcdc7edf644201b0b60
Reviewed-on: https://go-review.googlesource.com/33581
Reviewed-by: Dmitry Vyukov <dvyukov@google.com>
Reviewed-by: Russ Cox <rsc@golang.org>
5 files changed