MAR-161: Make the ldap_server_domain parameter in the ldap_server role mandatory:

- Updated the ldap_server role.
- Removed default value for the parameter.
- Updated tests.
- Updated role reference documentation.
- Updated release notes.
- Dropped the .local from the Molecule instance names.

MAR-150: Use fixtures for X.509 artefacts in the ldap_server role:

- Removed the statically generated artefacts.
- Generate X.509 artefacts for tests using Gimmecert.
- Updated paths to point to generated artefacts.
- Introduced cleanup playbook for removing generated artefacts.

MAR-162: Deduplicate TLS private key/certificate tests for LDAP server role:

- Rename the key/certificate files to match the Ansible inventory
name.
- Move the tests into test_default.py.
- Change the key/certificate extensions to be more descriptie.

MAR-162: Make the ldap_server_tls_certificate ldap_server_tls_key parameters mandatory:

- Updated release notes.
- Updated role reference documentation.
- Updated usage instructions to cover set-up of CA hierarchy earlier on
in the process.

MAR-129: Updated ldap_server role for new Molecule and Ansible:

- Fixed syntax warnings.
- Moved test playbook variables into group_vars.
- Optimised the invocation of test playbook.
- Remove the 'ss' utility from test machines in order to properly test
the unix sockets.
- Fixed how the hosts are being referenced in tests.