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
    
    (cherry picked from commit 467f7dcb3cead9ce736c1c6fd0518e8ae61faef6)