Upstream changes

[JayH5]

• Revert "dpkg-divert" and change PATH instead docker-library/python#137
• Add a few simple Python 3 templates based on existing Dockerfiles docker-library/python#139
• Add build-time headers/packages for "import dbm" to work properly on 2.7 slim and alpine variants docker-library/python#140

[calston]

👍