Remove input and output stream, that always pointed to sys.stdin
and sys.stdout.
Add tests for DoPostUploadExecuter.
Bug: 1042324
Change-Id: Ib5d092706a242ae97ec877af5dbceef6db7cbb73
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2079411
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>