Revert "Revert "roles/common: Use static imports for tasks""

This reverts commit 63c5477f85.

I'm actually still seeing this problem on Ansible 2.4.0.0 with Python
2.7.14.

roles/common/tasks/main.yml

@@ -5,11 +5,23 @@
   tags: ntp
 
 - name: Install common packages
-  include_tasks: packages_{{ ansible_distribution }}.yml
+  import_tasks: packages_Debian.yml
+  when: ansible_distribution == 'Debian'
+  tags: packages
+
+- name: Install common packages
+  import_tasks: packages_Ubuntu.yml
+  when: ansible_distribution == 'Ubuntu'
   tags: packages
 
 - name: Configure firewall
-  include_tasks: firewall_{{ ansible_distribution }}.yml
+  import_tasks: firewall_Debian.yml
+  when: ansible_distribution == 'Debian'
+  tags: firewall
+
+- name: Configure firewall
+  import_tasks: firewall_Ubuntu.yml
+  when: ansible_distribution == 'Ubuntu'
   tags: firewall
 
 - name: Configure secure shell daemon