Load configuration from the defined locations.

def load(self):
        """Load configuration from the defined locations."""
        if not self.loaded:
            self.values = configobj.ConfigObj({}, **self.DEFAULT_CONFIG_OPTS)
            for path in self.locations():
                try:
                    part = configobj.ConfigObj(infile=path, **self.DEFAULT_CONFIG_OPTS)
                except configobj.ConfigObjError as cause:
                    raise LoggedFailure("Error in file '{path}': {cause}".format(path=pretty_path(path), cause=cause))
                self.values.merge(part)
            self.loaded = True
        return self.values