demos/contrib/test_cf_ugrid3.m: Update URIs and use ncvariable-style dat...

Update URIs and use ncvariable-style data access for face_node_connectivity data.

Related to https://github.com/nctoolbox/nctoolbox/issues/36

I'm not sure if the COMT catalog is the best, but its works better than testbedapps-dev.

Also, the nface_node_connectivity is a ncvariable, rather than a ncgeovariable, so the matlab-syle access method fails.