Add integration for CircleCI.

Review Request #8951 — Created May 19, 2017 and submitted — Latest diff uploaded

Information

rbintegrations
master
92bed80...

Reviewers

This change adds a new integration which allows people to build prospective
changes via CircleCI. This requires the (beta) CircleCI 2.0.

This is similar in many ways to the Travis CI integration, but is somewhat
different in its configuration. The major difference is that while Travis
allows us to override the config within our API request, Circle does not. This
means that users will have to add Review Board support within their
.circleci/config.yml file.

When a config matches, this integration will trigger a build of the
"reviewboard" job (as defined in the user's config) and pass along various bits
of data in the build parameters.

Posted a variety of changes which should either fail or pass the build, and
saw the results reported correctly.