dashboard: add Cloud Storage upload support to create.go

Then make the coordinator and linux environment Makefiles have
an upload target. Amusingly, this actually worked: the Docker
images now tar + compress + upload over HTTP all in a stream,
without even knowing how large the resulting tar.gz will be until
it's done uploading.

LGTM=adg
R=adg
CC=golang-codereviews
https://golang.org/cl/140200043
5 files changed