Add Jenkinsfile
Add Jenkinsfile

This integrates the Jenkinsfile into the repo so that we can have
version-bound test configurations.

Older branches for example might not support the newest JDK.

EvilMcJerkface/crate,crate/crate,EvilMcJerkface/crate,EvilMcJerkface/crate,crate/crate,crate/crate