Use alias for repositories in KIWI config.xml

This does work around issues with SCC repositories in older KIWI
versions.
If the repository had no alias the repository name was generated by the
URL which was in case of SCC too long.
Add sles-release-DVD to package filtering for building

The package is only available on the DVD but not in the SCC repositories
so it needs to be filtered to be able to build an imge.