Flush handlers before marking a node schedulable after upgrade.

Handlers normally only trigger at the end of the play, but in this case
we just set our node schedulable again resulting in it immediately
getting taken down again.

playbooks/common/openshift-cluster/upgrades/upgrade.yml

@@ -211,6 +211,8 @@
   - include: containerized_node_upgrade.yml
     when: inventory_hostname in groups.oo_nodes_to_config and openshift.common.is_containerized | bool
 
+  - meta: flush_handlers
+
   - name: Set node schedulability
     command: >
       {{ openshift.common.admin_binary }} manage-node {{ openshift.common.hostname | lower }} --schedulable=true