Change sandbox machines to n1-standard-4 to reduce resource usage.

Author: thompsonja

test/cluster/sandbox/example_sandbox.yaml

@@ -17,7 +17,7 @@ sandbox:
       # command line or randomly generated name.
       name: {{cluster_name}}
       node_count: 5
-      machine_type: n1-standard-8
+      machine_type: n1-standard-4
   # Application is application-specific, used by the derived Sandbox class.
   application:
     vtgate_count: 1