Security improvement for docker

[pieterlukasse]

@fedde-s mentioned this part of https://docs.docker.com/engine/security/security/#linux-kernel-capabilities

As of Docker 1.10 User Namespaces are supported directly by the docker daemon. This feature allows for the root user in a container to be mapped to a non uid-0 user outside the container, which can help to mitigate the risks of container breakout. This facility is available but not enabled by default.

Would be good to add the right documentation steps (or links to it) in this repo to enable this & automate where possible.

[pieterlukasse]

@fedde-s maybe this issue can be moved to the cbioportal/cbioportal main repo? Or is it better to move it to our deployment docs?