presubmit_support: Refactor and add tests for DoPostUploadExecuter.

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>
diff --git a/git_cl.py b/git_cl.py
index 72cd32d..8cba728 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -1534,9 +1534,7 @@
         presubmit_support.DoPostUploadExecuter(
             change,
             self.GetGerritObjForPresubmit(),
-            settings.GetRoot(),
-            options.verbose,
-            sys.stdout)
+            options.verbose)
 
       # Upload all dependencies if specified.
       if options.dependencies: