FIX - Windows Docker file permissions

[carlwilson]

• use id utility to deduce running process uid and default group id for Docker chown command; and
• the container is still run in a single invocation with chained commands.

@bitsgalore, you probably don't need to do the PyPi thing for this but if you do I'd suggest a post release.

[carlwilson]

@bitsgalore, while it's not the reworking of the Docker flow we talked about, it's still a much more elegant solution and should ensure build artefacts are all given the calling users uid as owner and primary group id as group.