Fix matrix_dynamic_dns_domain_configurations validation check

- `item` was undefined
- `'key' in configurations == ''` was doing the wrong thing

Related to #681 (Github Pull Request)

roles/matrix-dynamic-dns/tasks/validate_config.yml

@@ -3,8 +3,8 @@
 - name: Fail if required settings not defined in configuration blocks
   fail:
     msg: >-
-      You need to define a required configuration setting (`{{ item }}`).
-  when: "'domain' not in configuration == '' or 'provider' not in configuration == '' or 'protocol' not in configuration == ''"
+      One of the configurations in matrix_dynamic_dns_domain_configurations is missing a required key (domain, provider, protocol).
+  when: "'domain' not in configuration or 'provider' not in configuration or 'protocol' not in configuration"
   with_items: "{{ matrix_dynamic_dns_domain_configurations }}"
   loop_control:
     loop_var: configuration