Add cleanup step for empty mocked role folders

[zhan9san]

Before

If we want to test one role based on another role, we can define the role name in molecule/[scenario-name]/requirements.yml and add it in mock_roles in .ansible-lint config file.

Assume the dependency role is zhan9san.test

One the role is defined in mock_roles in .ansible-lint file, ansible-lint would create an empty dir under ~/.cache/ansible-compat/9eeb38/roles/zhan9san.test.

molecule dependency does install the role defined in molecule/[scenario-name]/requirements.yml but under ~/.cache/molecule/ansible-role-test-lint/default/roles dir.

When we run molecule test, it will set ANSIBLE_ROLES_PATH=$runtime_cache_dir/roles:$ephemeral_directory/roles/:$project_directory/../:~/.ansible/roles:/usr/share/ansible/roles:/etc/ansible/roles referring to ANSIBLE_ROLES_PATH.

The first path $runtime_cache_dir/roles in ANSIBLE_ROLES_PATH is ~/.cache/ansible-compat/0ad53a/roles while the second $ephemeral_directory/roles/ is ~/.cache/molecule/ansible_role_example/default/roles.

As we know, the order of ANSIBLE_ROLES_PATH matters, and zhan9san.test does exist in first role path, so ansible will run it without error if it is an empty role.

After

Once the empty role dirs are deleted, ansible will choose the role under ~/.cache/molecule/ansible-role-test-lint/default/roles dir.

Reference: ansible/molecule#3610 (comment)

Fixes: #2234