Remove full paths from install destinations in cvmfs-config-cern rpm

cvmfs-config-cern rpm was including the full path of the SOURCES directory in the install path, since that's included in each %{SOURCEN} macro.  Instead, I suggest pre-creating the destination directories and use the directory name as the destination.  Then install will use the last component of the source path as the filename in the destination directory, just like cp, etc.  The other alternative is to use something like `basename` on the destination path.