Bundling packages not in the top level project directory but declared…

[justoy]

Bundling packages not in the top level project directory but declared in source_directories

Here is an example. The python module is not in the top level project directory. This pull request makes python-lambda bundle the sub_py_module.

project_root ├── source.py ├── sub_project │   ├── sub_py_module └── config.yaml

In config.yaml: build: source_directories: sub_project/sub_py_module