Add Azure Pipelines CI

[hugovk]

For #3606.

Changes proposed in this pull request:

• As a first step for CI Review #3606, here's a simple lint job for us to get the plumbing into place, the integration set up and some familiarity

• Now tox is used for linting in Travis CI (Add linting to the tox matrix #3578), it's simple to mirror the same steps here

• Here's an example of how it looks: https://dev.azure.com/hugovk/hugovk/_build/results?buildId=58

TODO:

• Someone with more permissions than me needs to install the Azure Pipelines GitHub App and set up this repo:
  • https://github.com/apps/azure-pipelines/installations/new
  • https://andrewlock.net/building-an-open-source-github-project-using-azure-devops/

[hugovk]

Updated to move the 11 Docker builds from Travis CI to Azure Pipelines.

It was quite straightforward to move this over, which of course is the whole point of Docker!

• The Azure Pipelines build takes 5-6 minutes for the 1+11 jobs.

• The Travis CI build goes from ~26 minutes for 24 jobs to ~13 minutes for 13 jobs.

And both CIs run in parallel, meaning all these Linux builds are now done in max(6, 13) == 13 minutes.

Notes:

Uses templates for the build matrix by passing in parameters:

- template: .azure-pipelines/jobs/test-docker.yml
  parameters:
    docker: 'ubuntu-trusty-x86'
    name:   'ubuntu_trusty_x86'

• docker is the Docker image pulled from the pythonpillow Docker Hub.
• name is the display name of the job, A-Z, a-z, 0-9, and underscore
  • Duplicates docker, but with dashes replaced with underscores
• dockerTag can be specified as well, but defaults to master
• vmImage is the base image used for running Docker on. Defaults Ubuntu-16.04, the most recent Ubuntu available

https://docs.microsoft.com/en-us/azure/devops/pipelines/yaml-schema?view=azure-devops&tabs=schema#job

TODO later:

• Also run .travis/after_success.sh for Azure Dockers to send coverage to Codecov

---

See also https://twitter.com/ReinH/status/1098663375985229825

[hugovk]

I had a go getting coverage working on Azure Pipelines in another branch but got a bit stuck getting all the pieces in place (problems with permissions creating coverage output with lcov and coveralls), so I've reverted the last commit ("Remove Docker builds from Travis CI").

Let's merge this then enable AP for the repo. We can't remove builds from Travis until coverage is sorted, but we will benefit from seeing build results sooner and learning how AP works.