Opening a multi variable NetCDF does not info anymore

[felixcremer]

Before #416 opening a NetCDF file with multiple variables opened the first valid variable but gave an info that it took the first and which it took.
Now it just takes the first and does not throw an info.
I think it would be good to reintroduce the info in the CDM opening path.

This is the info that was given:

[ Info: No `name` or `key` keyword provided, using first valid layer with name `:climatology_bounds`