Standardize "apt-get install" usage across the repo

I might have missed some, but I think this is most of the offenders.

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Accept vanilla Linux Foundation signoffs

This allows signing off commits with `git commit -s`

Docker-DCO-1.1-SIgned-off-by: Solomon Hykes <solomon@docker.com> (github: shykes)