Test Java 8 too on Azure Pipelines (#1033)

Since Azure Pipelines allows up to 10 concurrent jobs, we can easily afford to run a second one per push, and it can help us ensure we're not breaking compatibility with JDK 8 (which I think some plugins still require). This PR adds a second job on JDK 8, and renames the jars from that second job; I'm not sure why there's only one coverage report.
3 files changed