feat(*): introduce Jenkinsfile
feat(*): introduce Jenkinsfile

Introduce Jenkinsfile to use Jenkins Pipelines and track and test
different build/test configurations.
The current configuration will provision an agent using the `Dockerfile`
and then lint, build and test the UI.

Closes DCOS-12802

dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui,dcos/dcos-ui