- Remove mention of tests/requirements.yml from the Requirements section in the README, relevant only for testing.

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- Add pre-commit check for out-of-date dependencies.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.

  how to install roles.
- Corrected privilege escalation in tests, added example.

- Moved test SSH keypair to tests/files.
- Corrected error in Ansible 2.1 in case some users don't have a password hash
  set.

- Instead of treating root as a special case, handle it like any other user (see
  README.rst and tests/playbook.yml). Should also be handy for other users.