Run py3 compatible unit tests with py3
Run py3 compatible unit tests with py3

R=05bb588aa9020353543fee7ac4e6e0a3d0d6f6ed@google.com

Change-Id: Id5e4f99ccb9d284ac09c2c4dd0fa57e59cb54f49
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/3291894
Commit-Queue: Josip Sokcevic <4606aec58cba917397ff2e4738f995e4758694f8@google.com>
Reviewed-by: Anthony Polito <05bb588aa9020353543fee7ac4e6e0a3d0d6f6ed@google.com>

CoherentLabs/depot_tools,CoherentLabs/depot_tools