Given a source, find it.

        source can be a url or an index name.

def find_source(self, source):
        """
        Given a source, find it.

        source can be a url or an index name.
        """
        if not is_valid_url(source):
            try:
                source = self.get_source(name=source)
            except SourceNotFound:
                source = self.get_source(url=source)
        else:
            source = self.get_source(url=source)
        return source