use cipd_platform instead of os/arch where possible

The Swarming bot now exposes cipd_platform, which is very close to
$GOOS-$GOARCH. Use that instead.

This should be entirely a no-op, except for Solaris, which will start
working. I've spot checked a number of builders to verify that the
dimensions look good, but a second check wouldn't hurt.

Change-Id: I453cbfce815a81f7e48ca1b9897c632536ac48f2
Reviewed-by: Michael Knyszek <>
Auto-Submit: Heschi Kreinick <>
TryBot-Bypass: Heschi Kreinick <>
3 files changed