ConfigGenerator: generate module parent node dynamically instead of hardcoding

Taken from https://github.com/checkstyle/regression-tool/pull/43#discussion_r125323003

The `TreeWalker` node is hardcoding currently. We should generate these nodes dynamically. For each module, we should get its parent module via its `parent` field, and then search the parent module in the module extract info map. If there is no such parent, then throw an exception and stop the process, otherwise generate every node we need dynamically in this way.