Upgrade to Ubuntu 18.04 LTS

[hackdna]

Currently used version 16.04 LTS has end of life date April 2021
Ubuntu 18.04 LTS has end of life date April 2023
https://wiki.ubuntu.com/Releases

Python 3.5 (included in Ubuntu 16.04 LTS) end-of-life is 2020-09-13
Ubuntu 18.04 LTS comes with Python 3.6
https://devguide.python.org/#status-of-python-branches

Considerations:

• Travis CI support (replace with AWS CodeBuild?)
• OS service management (systemd)
• System package compatibility with Refinery dependencies
• Going from Python 3.5 (standard on 16.04) to Python 3.6

Resources:

• https://blog.travis-ci.com/2017-12-01-new-update-schedule-for-linux-build-images
• http://news.softpedia.com/news/ubuntu-devs-work-on-demoting-python-2-to-universe-repo-for-ubuntu-18-04-lts-518926.shtml
• https://www.reddit.com/r/programming/comments/atjltu/layoffs_at_travis_ci_their_team_was_being/

Requires: upgrade to Django 1.11 (#2572)

[drj11]

Apparently Travis CI only support Precise, 12.04, and Trusty, 14.04.

Should we have separate a separate issue for that?

[hackdna]

All three environments (dev: Vagrant, prod: AWS, CI: Travis) should be updated in sync. We may have to replace Travis with another CI system but I don't think it's necessary to have a separate issue for that.