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)
Merge pull request #7362 from crosbymichael/fix-get-image-json

Fix get image json
Merge pull request #7035 from tianon/standardize-apt-get-install

Standardize "apt-get install" usage across the repo
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)