This PR ensures that we're calling app.run() in a consistent way across all standard_python37 samples (including the comments).

There's a few other places where we might want to update as well, but I'm not familiar enough with these samples to say for sure that we should:

• python-docs-samples/auth/end-user/web/main.py

  Line 119 in 8f28cb6

  app.run('localhost', 8080, debug=True)

• python-docs-samples/iap/example_gce_backend.py

  Line 42 in 8f28cb6

  app.run()

• python-docs-samples/compute/xmpp_wikibot/wikibot.py

  Line 150 in 8f28cb6

  app.run(threaded=True, use_reloader=False, host='0.0.0.0', debug=False)