NFSAAS-2101 update schema for swagger 2019-05-01

Author: leonardbf

schemas/2019-05-01/Microsoft.NetApp.json

@@ -553,6 +553,9 @@
           "description": "The service level of the file system."
         }
       },
+      "required": [
+        "serviceLevel"
+      ],
       "description": "Pool properties"
     },
     "SnapshotProperties": {
@@ -665,4 +668,4 @@
       "description": "Set of export policy rules"
     }
   }
-}
+}