Extend the --product warning message

Make sure that users know that Workstation is GNOME and that the
$PRODUCT choices may install new packages.
Rename fedora-release-standard to fedora-release-nonproduct

It was properly obsoleted in Fedora, so either will work, but we
may as well use the correct current name here.
Merge pull request #52 from sgallagher/master

Extend the --product warning message