Fixes #6884 - Installation media without $minor generate broken $version

$version is generated with the major version and a dot, producing paths
like foo.bar/x64/7. which don't exist. For CentOS at least we want to generate
a path without the dot. The default values for these media have been changed too.

(cherry picked from commit 7560679b9849b0fc5c168d5047bd3469d719b45a)

Conflicts:
db/seeds.d/10-installation_media.rb