Fix CI (docker_container tests fail because of missing ipaddress) (#218)

* Use stdlib ipaddress, resp. install when needed.

* Make sure facts on controller are available.

tests/integration/targets/docker_container/tasks/main.yml

@@ -4,6 +4,19 @@
 # and should not be used as examples of how to write Ansible roles #
 ####################################################################
 
+- name: Gather facts on controller
+  setup:
+    gather_subset: '!all'
+  delegate_to: localhost
+  delegate_facts: true
+  run_once: true
+
+- name: Make sure ipaddress is available on controller
+  pip:
+    name: ipaddress
+  delegate_to: localhost
+  when: hostvars['localhost'].ansible_facts.python.version.major < 3
+
 # Create random name prefix (for containers, networks, ...)
 - name: Create random container name prefix
   set_fact: