ncm-named: fix retrieval of named root directory from sysconfig

Fixes #241

Wait for more unit tests to be added before merging this PR.
I'd prefer to wait a discussion at the next workshop about what we consider the appropriate policy before changing this. This would introduce a backward incompatibility for sites not relying on the template library (in the template library we may add the appropriate `ncm-chkconfig` config at the same time to compensate for the change). Fixing this when we agree will be easy: basically just remove the lines...