Draft: pkgctl repo clone: add error for nonexisting package

Single package

$ pkgctl repo clone apache2
==> Cloning apache2 ...
  x api call failed: 404 Project Not Found

Multiple packages

$ pkgctl repo clone apache apache2
pkgctl repo clone
0% 0:2=0s apache2                                                                                       
==> Cloning apache2 ...
  x api call failed: 404 Project Not Found
50% 1:1=1s apache2                                                                                      
==> Cloning apache ...
==> Collecting packager identity from makepkg.conf
  -> name    : undefined
  -> email   : undefined
  -> gpg-key : undefined
  -> protocol: https
==> Configuring apache
Cloning into 'apache'...
100% 2:0=0s apache2                                                                                     
==> ERROR: Failed to clone some packages, please check the output

Closes #151