This adds a job to test the UI on CircleCI, including the sort of branch
pattern-matching from #5839, so .-ui/ branches only have that job
and not the non-UI ones.
I considered having an entire workflow for UI, which could have separate
jobs for linting vs Ember tests, but the lint commands take so little time
that it didn’t seem worth it.
There’s no use of nvm to change the Node version as the Docker image
is what controls that. It’s annoying to have to update the version in multiple
places, but probably infrequent.
This commit provides an initial migration of general testing CI
infrastructure to CircleCI.
It uses CircleCI 2.1 paramereterised jobs to provide two base
configurations: a vm based `test-machine`, and docker based
`test-container`.
Jobs that require root, docker, or other similar features require the
machine based jobs, but others should be ran using the `test-container` package
as they are both cheaper and faster to run.
