Download sysroot from "commondatastorage.googleapis.com"

For some reason our intranet here is blocking googleapis.com.
Actually other tools that are updated via runhooks are using
that alias url already (e.g. clang).

Review URL: https://codereview.chromium.org/1534873002

Cr-Commit-Position: refs/heads/master@{#366481}
1 file changed