Use pod uid as instance uuid

Inject the pod uid as an environment variable and use it for the
SYSTEM_UUID in the settings file defined by the configmap.

installer/roles/kubernetes/templates/deployment.yml.j2

@@ -285,6 +285,10 @@ spec:
           env:
             - name: AWX_SKIP_MIGRATIONS
               value: "1"
+            - name: MY_POD_UID
+              valueFrom:
+                fieldRef:
+                  fieldPath: metadata.uid
           resources:
             requests:
               memory: "{{ task_mem_request }}Gi"