Add hadolint checker

[fauust]

Fix some warnings/errors

[grooverdan]

There should be a note about the impact of --no-install-recommends in the commit message.

Targetting next branch so that it gets buildbot testing before release.

[fauust]

There should be a note about the impact of --no-install-recommends in the commit message.

Yep, indeed, good catch. I was not sure about it and forget to mention. We can also remove it and skip this check.

[grooverdan]

Add the ignore for now. I didn't see anything in Recommends obviously used, but would rather consider it later.

[grooverdan]

Thank you.