revert scability master back to n1 machines

Author: kannon92

config/jobs/kubernetes/sig-scalability/sig-scalability-presets.yaml

@@ -274,7 +274,7 @@ presets:
   env:
   # Override GCE defaults.
   - name: MASTER_SIZE
-    value: "e2-standard-4"
+    value: "n1-standard-4"
   - name: NODE_SIZE
     value: "e2-standard-8"
   - name: NODE_DISK_SIZE