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/common/templates/tarsnap_sources.list.j2

@@ -1,4 +1,4 @@
-{% 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 https://pkg.tarsnap.com/deb/artful ./
 {% else %}