Code review comment for lp://staging/~jani/ubuntu-system-image/skip-gpg-verification

I'm going to implement this a little differently, but I'll get the feature in.

One question: I could disable this flag if system-image-dev binary package isn't installed. That would make me feel better, but I'm guessing that won't work for you because you're testing on live devices (and normally, devices do not have that package installed).

Alternatively, we could hide --skip-gpg-verification from the --help output and/or the system-image-cli manpage. Is that worth it?