Remove hardcoded build-server hostname

Previously cobbler config was locked to the hostname
builde-server. Since none of this config will clash
on other nodes, as they do not include the appropriate
classes, this data can safely be moved to the common
yaml files.

Change-Id: Ife354e63fcafcf447931b9d387bee1cc9fb8b147
Merge "Remove hardcoded build-server hostname"