Support nested modules with ANSIBLE_LIBRARY env var

This PR adds support to look for modules in nested directories when using `ANSIBLE_LIBRARY`.

Due to ansible now using git submodules, I don't init the submodules for dev purposes.  Instead I have my own forks cloned, and I use:

```
export ANSIBLE_LIBRARY=/Users/matt/python_venvs/ansibledev/ansible-modules-core:/Users/matt/python_venvs/ansibledev/ansible-modules-extras
```

Currently, when using ansible set up this way, ansible fails to find any modules:

```
localhost | FAILED => module rax not found in configured module paths
```