fix(hardware-testing): add __init__.py to modules/ so it gets packed in the build + other Flex stacker QC fixes.

[vegano1]

Overview

Sdist does not package non-module directories, so lets add an __init__.py so it does, this will make it so we can push to the robot. Fix some additional issues found while testing the Flex stacker QC script.

Test Plan and Hands on Testing

• Make sure we can use push-ot3 and run the flex_stacker_qc_script from the flex robot.
• Makes sure the flex_stacker_qc_script run successfully and on a real Flex-stacker

Changelog

• add __init__.py to /modules dir
• change the way we validate no movement when in e-stop
• don't wait for ack from stop_motor M0 command.

Review requests

Risk assessment

[djgomez-opentrons]

tested on 2 stackers, works