Fixed fallback to internal geocoder in nameplaces geocoding functions
Fixed fallback to internal geocoder in nameplaces geocoding functions

- Fixed fallback becuase we have to use spiexceptions in this case
because we retrieve the configuration usig plpy.execute fuctions that
wrap any exception into a spiexception.

- In case we don't want to use Mapzen, we could leave the api_key empty
becuase we arise a ConfigException if the Mapzen api_key is empty so
we are able to make fallback. Right now we can't remove the mapzen
configuration because it'll fail when the InternalGeocoderConfig try to
load the ServiceDBConfig

This is a dirty hack, we should improve how the DB config is loaded. See

CartoDB/geocoder-api,CartoDB/geocoder-api,CartoDB/dataservices-api,CartoDB/geocoder-api,CartoDB/dataservices-api,CartoDB/dataservices-api,CartoDB/dataservices-api,CartoDB/geocoder-api