Dockerfile refactor

[serl]

Hello, I refactored a little bit the Dockerfile following some best practices:

• using a fixed base image version
• running as non-root user
• and as a bonus, I added FF_VER as build argument

Probably the travis configuration should be updated as well.

Thanks!

[anthwlock]

Hey, thank you! I have pushed your commit and some additional changes on new_docker. The Makefile uses git for determining untrunc's version, so it needs to be installed.

By using multi-stage builds I managed

• shared lib: 540MB -> 200MB
• local lib: 900MB -> 115MB

But since docker keeps previous stages for caching, they have be deleted explicitly.

It looks like rm -rf /var/lib/apt/lists is not needed:

Note: The official Debian and Ubuntu images automatically run apt-get clean, so explicit invocation is not required.

[serl]

Wow, great job!

I think rm -rf /var/lib/apt/lists is still needed. If I understood correctly, apt-get clean will not remove that directory: https://askubuntu.com/a/894822.

[anthwlock]

You were right, images are now 20MB smaller. Thanks!