Make roles more independent of one another

With this change, the following roles are now only dependent
on the minimal `matrix-base` role:
- `matrix-corporal`
- `matrix-coturn`
- `matrix-mailer`
- `matrix-mxisd`
- `matrix-postgres`
- `matrix-riot-web`
- `matrix-synapse`

The `matrix-nginx-proxy` role still does too much and remains
dependent on the others.

Wiring up the various (now-independent) roles happens
via a glue variables file (`group_vars/matrix-servers`).
It's triggered for all hosts in the `matrix-servers` group.

According to Ansible's rules of priority, we have the following
chain of inclusion/overriding now:
- role defaults (mostly empty or good for independent usage)
- playbook glue variables (`group_vars/matrix-servers`)
- inventory host variables (`inventory/host_vars/matrix.<your-domain>`)

All roles default to enabling their main component
(e.g. `matrix_mxisd_enabled: true`, `matrix_riot_web_enabled: true`).
Reasoning: if a role is included in a playbook (especially separately,
in another playbook), it should "work" by default.

Our playbook disables some of those if they are not generally useful
(e.g. `matrix_corporal_enabled: false`).

roles/matrix-nginx-proxy/tasks/ssl/main.yml

@@ -8,15 +8,6 @@
 
 # Common tasks, required by any method below.
 
-- name: Determine domains that we require certificates for (Matrix)
-  set_fact:
-    domains_requiring_certificates: "['{{ hostname_matrix }}']"
-
-- name: Determine domains that we require certificates for (Riot)
-  set_fact:
-    domains_requiring_certificates: "{{ domains_requiring_certificates + [hostname_riot] }}"
-  when: "matrix_riot_web_enabled"
-
 - name: Ensure SSL certificate paths exists
   file:
     path: "{{ item }}"

roles/matrix-nginx-proxy/tasks/ssl/setup_ssl_lets_encrypt.yml

@@ -39,7 +39,7 @@
 
 - name: Obtain Let's Encrypt certificates
   include_tasks: "{{ role_path }}/tasks/ssl/setup_ssl_lets_encrypt_obtain_for_domain.yml"
-  with_items: "{{ domains_requiring_certificates }}"
+  with_items: "{{ matrix_ssl_domains_to_obtain_certificates_for }}"
   loop_control:
     loop_var: domain_name
   when: "matrix_ssl_retrieval_method == 'lets-encrypt'"

roles/matrix-nginx-proxy/tasks/ssl/setup_ssl_manually_managed.yml

@@ -2,7 +2,7 @@
 
 - name: Verify certificates
   include_tasks: "{{ role_path }}/tasks/ssl/setup_ssl_manually_managed_verify_for_domain.yml"
-  with_items: "{{ domains_requiring_certificates }}"
+  with_items: "{{ matrix_ssl_domains_to_obtain_certificates_for }}"
   loop_control:
     loop_var: domain_name
   when: "matrix_ssl_retrieval_method == 'manually-managed'"

roles/matrix-nginx-proxy/tasks/ssl/setup_ssl_self_signed.yml

@@ -18,7 +18,7 @@
 
 - name: Generate self-signed certificates
   include_tasks: "{{ role_path }}/tasks/ssl/setup_ssl_self_signed_obtain_for_domain.yml"
-  with_items: "{{ domains_requiring_certificates }}"
+  with_items: "{{ matrix_ssl_domains_to_obtain_certificates_for }}"
   loop_control:
     loop_var: domain_name
   when: "matrix_ssl_retrieval_method == 'self-signed'"