Use example node pool names for affinity argument (#1601)

I believe this will make it clearer what the actual value should be for the affinity label.

Author: tswast

composer/workflows/kubernetes_pod_operator.py

@@ -160,8 +160,8 @@
                             # The label key's value that pods can be scheduled
                             # on.
                             'values': [
-                                'nodepool-label-value',
-                                'nodepool-label-value2',
+                                'node-pool-name-1',
+                                'node-pool-name-2',
                             ]
                         }]
                     }]