cvmfs: use metaconfig and make the code more generic

CVMFS configuration currently relies on `ncm-filecopy` to produce file that would be better managed by `ncm-metaconfig` (key/value pairs).

Also there is currently different hashes to describe the configuration of different CVMFS servers. We should try to have something more generic, allowing a site to add its specific servers, if any, without changing the code.
