Convert /etc/cobbler/version from Yaml to ConfigParser filetype.

This was required to get rid of the buildtime dependency on python-yaml.
PyYAML is not available on the Open Build Service (OBS) for EL6.
Now it's possible to directly provide packages/repos to our users (#737).
Merge pull request #753 from jmaas/remove-yaml-build-dep

Convert /etc/cobbler/version from Yaml to ConfigParser filetype.