- switched to cmake based build.

  This allow me to continue optimize build process and make it
  work for all my existing python projects.

  Old Makefile is not easy to update at all.

  deb pkg now include venv instead of wheels. no bootstrap needed.

- removed some obsolete scripts in utils/
- removed upstart configs
- removed utils/choose_default_python.sh, just use python3 from PATH
- app.yaml
  - use Amazon ECR by default
  - enable livenessProbe by default
- fabfile now use de04 as default PROD_HOST

- use python3 venv module to replace old bundled virtualenv module.
- upgrade docker build image and runtime image to debian buster based.
- bugfix: venv cache dir includes python version in dir name.

add Makefile for gocd integration