lookup adapter "lookup_global" produces bad error message for faulty hiera.yaml

When there is something wrong with the yaml syntax in a hiera.yaml the error message produced by the logic in lookup_adapter.lookup_global is not very helpful. It shows the error message twice, the reference to the faulty file says <unknown>, and the stack trace that is produced is for the location in the lookup_adapter, not where the error occurred.

To trigger the error use a hiera yaml with a hierachy like this:

:hierarchy:

  - %{boom}

(error is that there should be quotes around the entry)

The error can look like this:

Error: Could not run: Error from DataBinding 'hiera' while looking up 'lookup_options': (<unknown>): found character that cannot start any token while scanning for the next token at line 3 column 11 in (<unknown>): found character that cannot start any token while scanning for the next token at line 3 column 11

I think this is of importance to fix since it provides no clue to the user where the error may be.