Ensure systemd services are running when doing --tags=start

Fixes #129 (Github Issue).

Unfortunately, we rely on `service_facts`, which is only available
in Ansible >= 2.5.

There's little reason to stick to an old version such as Ansible 2.4:
- some time has passed since we've raised version requirements - it's
time to move into the future (a little bit)
- we've recently (in 82b4640072) improved the way one can run
Ansible in a Docker container

From now on, Ansible >= 2.5 is required.

roles/matrix-base/tasks/sanity_check.yml

@@ -3,10 +3,10 @@
 - set_fact:
     matrix_ansible_outdated_fail_msg: "You are running on Ansible {{ ansible_version.string }}, which is not supported. See our guide about Ansible: https://github.com/spantaleev/matrix-docker-ansible-deploy/blob/master/docs/ansible.md"
 
-- name: Fail if running on Ansible < 2.4
+- name: Fail if running on Ansible < 2.5
   fail:
     msg: "{{ matrix_ansible_outdated_fail_msg }}"
-  when: "ansible_version.major <= 2 and ansible_version.minor < 4"
+  when: "ansible_version.major <= 2 and ansible_version.minor < 5"
 
 # Ansible 2.5.0 and 2.5.1 are known to have a bug with `include_tasks` + `with_items`.
 # The bug has been fixed in Ansible 2.5.2.