MAR-128: Upgraded tests for ldap_server role:

- Switch to new Molecule configuration.
- Updated set-up playbook to use become: yes.
- Moved some preparatory steps outside of the main playbook (eases
idempotence tests).
- Updated tests to reference the yml inventory file.
- Updated tests to use new fixture (host instead of individual ones).
- Fixed some linting issues.
- Use localhost as backup client server name. This should make it
simpler in future to cover more platforms.
- Set-up the /etc/hosts for tests with correct entries (primarily
aliases towards localhost to make it less important what the
hostname is).
- Renamed private key/certificate files for parameters-mandatory
server since server got renamed as well.
- Updated IP addresses used for testing to make it easier to test new
platforms in the future.
- Use inventory_hostname-based parameterisation of tests where
appropriate. Currently hard-coded value for this because
host.ansible.get_variables() produces errors.