Improve Error output when file input specifier is missing

[landauermax]

trafficstars

When missing the file: specifier in the LogResourceList, the current error looks like:

Unsupported schema in LogResourceList: {'url': b'/home/landauerm/videoserver/logs/error.log.1', 'parser_id': 'ApacheErrorParsingModel', 'json': None, 'xml': None}

It is not obvious from this error that the url should look like file:///home/landauerm/videoserver/logs/error.log.1 instead. The error message should be improved to make this clear, since it is very easy to miss the specifier.