Add update step to 'plain' command

This patches sync the usage documentation for `all` and `all_noreboot` to indicate when they are expanded the update steps are ran.

Also it makes `plain` command consistent with `all` and `all_noreboot`.
Nope, objection!
"plain" should be nothing more than a plain installation. Please don't break it for anybody.
Rather create "plain_withupdate".