[pinpoint] enable py3 tests on handlers/commit
[pinpoint] enable py3 tests on handlers/commit

Also updated the existing tests:
 - add checks on how args are used
 - throw on the correct call
 - work for both webapp2 and flask.

Bug: chromium:1120195
Change-Id: I5a252c4f3ad580f4e2d71b0581b973394930281f
Reviewed-on: https://chromium-review.googlesource.com/c/catapult/+/3782576
Commit-Queue: Wenbin Zhang <45ad8a1ff616a38a2202fd35571df81897c5f14f@google.com>
Reviewed-by: John Chen <334fbfbb4df7c78f091ea1b77c69ca6ac731a3f3@chromium.org>

catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult,catapult-project/catapult