x/tools/dashboard/app: respect gohash in Commit.AddResult
x/tools/dashboard/app: respect gohash in Commit.AddResult

This should fix the issue where results sub-repo results are clobbered
by subsequent commits. (Much like the previous fix, which only
fixed the issue for main repo commits.)

TBR=bradfitz
R=bradfitz
CC=golang-codereviews
https://codereview.appspot.com/167440044

karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools,karmakaze/go.tools