* update python.gunicorn.sh to WEB_CONCURRENCY.sh
* don't remove WEB_CONCURRENCY for prefixed 0s
* split gunicorn functionality into its own file
* cleanup comments
* fix var ordering
* add retry to curl
* use proper url for buildpack stdlib
The Node buildpack now exports a leading zero in its numbers. This lets us detect that it (or another buildpack) set the value, and overwrite it accordingly.
Fixes the issue where adding the node buildpack to a Python app would cause only one gunicorn worker to be spawned for a 1X dyno, and not two.
We also need to again produce leading zeroes in the value, so that e.g. the PHP buildpack can do the same on boot.