Related to OTHER-338
A list of steps required to upgrade the point release of python in our various docker images. I'm listing it here for others to double-check and ensure that we've not missed any projects that use our images:

• Upgrade python 2.7 to 2.7.15
• Upgrade python 3.6 to 3.6.8
• Add python 3.7.2 docker image
• Delete 3.5 docker image from https://github.com/metabrainz/docker-python
  • Consider deleting old images for 3.6 and 2.7 here too
• Push 2.7.15 as metabrainz/python:2.7-2
• Push 3.6.8 as metabrainz/python:3.6-2
• Push 3.7.2 as metabrainz/python:3.7-1

• Migrate projects to new versions of images, using https://github.com/search?q=%22FROM+metabrainz%2Fpython%3A3.5%22&type=Code as a list:
  • acousticbrainz: switch to metabrainz/python:2.7-2
  • brainzutils-python: Switch python 2 to 2.7-2 (Dockerfile.py2), python 3 to 3.6-2 (Dockerfile.py3 and Dockerfile.pylint)
  • coverart_redirect: switch to metabrainz/python:3.6-2
  • critiquebrainz: switch to metabrainz/python:3.6-2
  • listenbrainz: switch to metabrainz/python:3.6-2
  • mb2wikidatabot: switch to metabrainz/python:2.7-2
  • mbspotify: switch to metabrainz/python:3.6-2
  • messybrainz-server: switch to metabrainz/python:3.6-2
  • metabrainz.org: switch to metabrainz/python:3.6-2
  • sir: switch to metabrainz/python:2.7-2

Open question: Do we switch directly to 3.7 now for all of our python 3 projects, or leave them on 3.6 until the maintainer can check and do the upgrade in their own time?

Open question 2: Do we bump another version of the metabrainz base images (https://github.com/metabrainz/base-image and https://github.com/metabrainz/docker-consul-template-base) in order to get a newer version of the phusion base images + updates to ubuntu packages, or is this just asking for trouble?)