Create SLES packages and serve them from the package server

Continued from #1081 (closed) .

To do:

1. Create a SLES Docker builder image. This is a bit more involved due to the way repositories get added to SLES OS's (mounting .iso)
2. Add support for sles platform to ohai_helper.rb
3. In .gitlab.ci.yml add sections to build sles packages and push to package repository