Improve error message readability

			panic(fmt.Errorf("error expanding config variable %s: %s", k, err))

		}

		if len(expandedVar) > 1 {

			panic(fmt.Errorf("%s expands to more than one string value: %s", variableValue, expandedVar))

			panic(fmt.Errorf("%q expands to more than one string value: %q", variableValue, expandedVar))

		}

		ret = append(ret, bazelConstant{

			variableName:       k,