This is a reland of commit eb16430c

Original change's description:
> Use io.open for opening files
>
> Use io.open which is consistent in py2 and py3.
>
> Bug: 1357152
> Change-Id: I49a3df503026bc6918362a9b5600f57111111111
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3872429
> Reviewed-by: Gavin Mak <gavinmak@google.com>
> Commit-Queue: Josip Sokcevic <sokcevic@google.com>

Bug: 1357152
Change-Id: I58881c040ca7333f0247875a0c4abe31cf793b08
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3877645
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Gavin Mak <gavinmak@google.com>