alpine + consul + openjdk image

[jousby]

Hi,

Similar to @rbellamy in issue #62. I'm keen to see a alpine + consul + openjdk image for running jvm based microservices.

I think the s6 overlay + consul plumbing in these images is really neat and hope these images have a long term future. I would be willing to help out on the openjdk image maitenance.

I'll raise a PR that basically takes @rbellamy 's openjdk PR and layers it on top of the alpine-consul-base image.