Include object validation in 3.6 upgrades

Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1428934

playbooks/common/openshift-cluster/upgrades/v3_6/validator.yml

@@ -7,4 +7,6 @@
   hosts: oo_first_master
   roles:
   - { role: lib_openshift }
-  tasks: []
+  tasks:
+  - name: Check for invalid namespaces and SDN errors
+    oc_objectvalidator: