Make self-check not validate self-signed certificates

By default, `--tags=self-check` no longer validates certificates
when `matrix_ssl_retrieval_method` is set to `self-signed`.

Besides this default, people can also enable/disable validation using the
individual role variables manually.

Fixes #124 (Github Issue)

roles/matrix-synapse/tasks/self_check_client_api.yml

@@ -4,6 +4,7 @@
   uri:
     url: "{{ matrix_synapse_client_api_url_endpoint_public }}"
     follow_redirects: false
+    validate_certs: "{{ matrix_synapse_self_check_validate_certificates }}"
   register: result_matrix_synapse_client_api
   ignore_errors: true
 

roles/matrix-synapse/tasks/self_check_federation_api.yml

@@ -4,7 +4,7 @@
   uri:
     url: "{{ matrix_synapse_federation_api_url_endpoint_public }}"
     follow_redirects: false
-    validate_certs: false
+    validate_certs: "{{ matrix_synapse_self_check_validate_certificates }}"
   register: result_matrix_synapse_federation_api
   ignore_errors: true