atomic: enable gpg verification after install
Taking the first step towards enabling gpg verification for our
users we'll make it so that the media they download will verify
gpg signatures of commits by default.
The next step is to enable gpg verification during install as well
but there is a race condition where the commit that was just created
might not yet be signed. See [1] for more details.
[1] https://pagure.io/pungi/issue/650