Don't stop containers before docker package update

Back in Openstack Pike release we hit issue with docker having
changes applied via puppet causing restart of docker service
without --live-restore option. This approach was buggous from the
begining and it's definetly obsolete here. We do only minor updates of
OS during release so we do only patch level updates of docker.

Change-Id: Iff4823d72c4d50838b6997398b23e76cec50ca56
RefBug: #1747851
Closes-Bug: #1851872

tasks/docker-update.yml

@@ -26,12 +26,6 @@
     - name: set docker_rpm_needs_update fact
       set_fact: docker_rpm_needs_update={{ docker_check_update.rc == 100 }}
 
-    - name: stop all containers before update
-      # xargs is preferable to docker stop $(docker ps -q) as that might generate a
-      # a too long command line
-      shell: docker ps -q | xargs --no-run-if-empty -n1 docker stop
-      when: docker_rpm_needs_update
-
     - name: ensure docker is installed
       package:
         name: docker