Ansible-playbook-grapher

- Fix playbook with relative var_file. Fix 35
- Add dependant bot to the repo:
- Update Pytest to 5.4.2
- Update graphviz to 0.14

- Update dependencies ([\29](https://github.com/haidaraM/ansible-playbook-grapher/pull/29))
- Make sure that an element exists before assigning
it ([\26](https://github.com/haidaraM/ansible-playbook-grapher/pull/26))

- Add support for Ansible 2.9 ([\25](https://github.com/haidaraM/ansible-playbook-grapher/pull/25))

Fix issue [\18](https://github.com/haidaraM/ansible-playbook-grapher/issues/18) with Ansible 2.8: the CLI was
refactored in https://github.com/ansible/ansible/pull/50069.
See https://github.com/haidaraM/ansible-playbook-grapher/pull/19 for the related changes.

- The grapher now requires Ansible >= 2.7.0
- New Feature: Add the support for include_role, import_role, import_playbook
- Fix https://github.com/haidaraM/ansible-playbook-grapher/issues/16
- Add more tests
- CLI more verbose: `-v` or `-vv` etc...
- Add `.dot` extension to graphviz exported file (option `-s`)
- ...

- Fix: Return code of the script