Also, add more failure output to debug why linux/mips64le and
linux/ppc64 are failing. They should be working. I suspect their
builder test envs are missing something.

Change-Id: I97273fe72c4e3009db400394636d0da1ef147485
Reviewed-on: https://go-review.googlesource.com/20358
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Ian Lance Taylor <iant@golang.org>