This changes benchsave to behave like benchstat; in addition to
uploading the files and printing a URL, it also prints the text format
of benchstat. This is fetched from the ViewURL provided by the storage
server, so the analysis can be changed/improved without requiring
users to rebuild benchsave.

Change-Id: I28519a5e3cf89962bd952ff26a8a6a717b9ef636
Reviewed-on: https://go-review.googlesource.com/37532Reviewed-by: Russ Cox <rsc@golang.org>