Allow container to run as non root

[raidenii]

Hi,

Please allow the container to run as non root user. The current Dockerfile WORKDIR /root prevents even --user arg when running the container as non root. Changing it to WORKDIR /tmp still builds the image successfully. Happy to submit a PR for that (and also remove dependency on openssl - for verifying the digest file, alpine image comes with sha512sum).

Also, is there a particular reason that this container need to run as root? By default, to bind port > 1024, any process can do, and /dev/shm is open for all for domain sockets. Even when the container needs to bind at port 443 on host, it can still be done via docker-proxy to redirect the port binding, and use high ports inside the container.

[kslr]

In most cases, tls etc, external port 443 is must required

[raidenii]

OK - my point still stands.

This PR simply allows one to run the container using --user argument, by which one can specify a non-root user to run it (e.g., nobody). If not specified, the container still runs as root inside and out, which allows it to bind to port 443.

Also, as I pointed out, one can run the container as nobody, and in config file binding the port to say, 10086, but use something like -p 443:10086 to map it to 443 on host.