docker_swarm_service: Add placement_preferences option (#51082)

* Add placement_preferences option

* Add changelog fragment

* Python 2.6 compat

Python 2.6 compat

* Cleaner check

* Better description

* Don’t compare placement_preferences if None

* Add placement_preferences example

test/integration/targets/docker_swarm_service/tasks/tests/options.yml

@@ -950,6 +950,46 @@
       - networks_2 is not changed
       - networks_3 is changed
 
+####################################################################
+## placement_preferences ###########################################
+####################################################################
+
+- name: placement_preferences
+  docker_swarm_service:
+    name: "{{ service_name }}"
+    image: alpine:3.8
+    placement_preferences:
+      - spread: "node.labels.test"
+  register: placement_preferences_1
+
+- name: placement_preferences (idempotency)
+  docker_swarm_service:
+    name: "{{ service_name }}"
+    image: alpine:3.8
+    placement_preferences:
+      - spread: "node.labels.test"
+  register: placement_preferences_2
+
+- name: placement_preferences (change)
+  docker_swarm_service:
+    name: "{{ service_name }}"
+    image: alpine:3.8
+    placement_preferences:
+      - spread: "node.labels.test2"
+  register: placement_preferences_3
+
+- name: cleanup
+  docker_swarm_service:
+    name: "{{ service_name }}"
+    state: absent
+  diff: no
+
+- assert:
+    that:
+      - placement_preferences_1 is changed
+      - placement_preferences_2 is not changed
+      - placement_preferences_3 is changed
+
 ####################################################################
 ## publish #########################################################
 ####################################################################

test/integration/targets/docker_swarm_service/vars/main.yml

@@ -21,6 +21,7 @@ service_expected_output:
   mode: global
   mounts: []
   networks: []
+  placement_preferences: null
   publish:
     - {mode: null, protocol: tcp, published_port: 60001, target_port: 60001}
     - {mode: null, protocol: udp, published_port: 60001, target_port: 60001}