Don't output complex items in the summary line

When iterating over complex objects, printing them out in the task
summary line is very noisy and hard to follow.

Change-Id: I4ae748f167ee03ba97a4bcbf2417dae0271e24a5

playbooks/zuul-stream/fixtures/test-stream.yaml

@@ -20,6 +20,13 @@
         - item2
         - item3
 
+    - name: Loop with complex items
+      command: "echo {{ item.name }}"
+      with_items:
+        - name: complex1
+        - name: complex2
+        - name: complex3
+
     - name: Run a shell task with an ansible python exception
       command: echo foo
       args: