jaeger-all-in-one: non-root permissions on /tmp

[beyang]

This addresses #559 (comment)

Post-merge:

• Move Docker images to https://github.com/sourcegraph/sourcegraph/tree/master/docker-images

[emidoots]

Note: when you move this over, you should use an almost identical build.sh as https://github.com/sourcegraph/sourcegraph/blob/master/docker-images/grafana/build.sh

This will ensure the image gets built on CI automatically, as well as that it gets versioned alongside Sourcegraph (jaeger-all-in-one:3.15.0 / jaeger-all-in-one:insiders NOT jaeger-all-in-one:1.17.1).

You should also make sure your Dockerfile has these labels: https://github.com/sourcegraph/sourcegraph/blob/master/docker-images/prometheus/Dockerfile#L20-L30