- Removed piprot dependency since it's used only with pre-commit and now it's installed inside the hook's virtualenv.

- Stop testing with Docker containers, they're only a good fit for a very limited use (cli applications, not services or system-level) and the speed of testing doesn't justify the work needed.

- Removed `--quiet` from the piprot check to see which packages are out
of date (check still works the same).
- Test on Python 3.5 and not 3.4 because Ansible is tested on 3.5 and
later.

accordingly.

- Add pre-commit check for out-of-date dependencies.
- Add flake8 pre-commit check.
- List roles needed for testing (bootstraping) at
tests/requirements.yml, leave other dependencies at meta/main.yml.
- Update molecule.yml, ansible.cfg for newer versions of Molecule.
- Update documentation, playbook accordingly.