Implement tests for preseed role.

The following should be done:

• Use Molecule for automating VM provisioning and running tests.
• Switch to using pip-tools for setting-up the development environment.
• Introduce initial documentation describing how to run tests etc.
• Update tasks as necessary to pass Ansible Lint checks. Introduce the skip_ansible_lint tag on relevant tasks where linting should be skipped.
• Apply minimal fixes to issues discovered during testing.
• When creating the tests, keep in mind the following:
  • Optional parameters should be tested.
  • Network settings generated via preseed role include two possibilities - DHCP and static. Make sure both are teted.
  • Per-host option overrides should be tested.
  • Due to relative complexity of testing the preseed files, this can be skipped for now, but documentation should clearly state this. Create a separate issue for this type of test.
  • Test both Debian Jessie and Debian Stretch (64-bit in both cases).