Fix a few more Jinja2 filters used as tests

I had created these earlier in this branch before rebasing it on top
of the Ansible 2.5.0 readiness branch.

See: https://docs.ansible.com/ansible/devel/porting_guides/porting_guide_2.5.html

roles/mariadb/templates/mariadb.list.j2

@@ -1,7 +1,7 @@
 # {{ ansible_managed }}
 {% if ansible_distribution == 'Ubuntu' %}
 
-{% if ansible_distribution_version | version_compare('18.04', '==') %}
+{% if ansible_distribution_version is version_compare('18.04', '==') %}
 # 2018-03-17: no Ubuntu 18.04 "bionic" packages yet, so use 17.10 "artful"
 deb [arch=amd64,i386] http://mariadb.mirror.serveriai.lt/repo/10.2/ubuntu artful main
 {% else %}