This is a reland of 310e1e81

Use subprocess2, which will set shell=True when running on Windows.

Original change's description:
> metrics: Use vpython3 instead of sys.executable
>
> Apparently, uploading metrics might happen after sys.executable
> has been deleted.
>
> Bug: 1068263
> Change-Id: Id4ab465bb97d146b688f42fb2002e29372e65555
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2148879
> Commit-Queue: Anthony Polito <apolito@google.com>
> Reviewed-by: Anthony Polito <apolito@google.com>

Bug: 1068263
Change-Id: I19c915f3e8862ae3248b01e0eccdbdf0bfda7369
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2150170Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>