milo: Use service interface for swarming.

milo/appengine/swarming/expectations/build-canceled.json

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     "ParentLabel": {
       "Label": "infra-continuous-precise-32",
       "URL": "/buildbucket/estaab-infra-waterfall-test/infra-continuous-precise-32?server=cr-buildbucket-dev.appspot.com"
     },
     "Label": "2d8d62f6be545b10",
     "Status": "Failure",
     "Banner": {
       "OS": [
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           "Img": "ubuntu.svg",
           "Alt": "Canonical Ubuntu",
           "Subtitle": "12.04",
           "Count": 1
         }
       ],
       "Device": null
     },
     "Bot": {
       "Label": "swarm3-c4",
-      "URL": "https://debug/restricted/bot/swarm3-c4"
+      "URL": "https://example.com/restricted/bot/swarm3-c4"
     },
     "Source": {
       "Label": "Task 2d8d62f6be545b10",
-      "URL": "https://debug/user/task/2d8d62f6be545b10"
+      "URL": "https://example.com/user/task/2d8d62f6be545b10"
     },
     "MainLink": {
       "Label": "Task 2d8d62f6be545b10",
-      "URL": "https://debug/user/task/2d8d62f6be545b10"
+      "URL": "https://example.com/user/task/2d8d62f6be545b10"
     },
     "SubLink": [
       {
         "Label": "stdout",
         "URL": "foo/stdout"
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     ],
     "Progress": null,
     "Started": "2016-03-14T10:00:01.85071Z",
     "Finished": "2016-03-14T11:00:18.48602Z",
@@ skipping 161 matching lines @@
         },
         {
           "Key": "allow_milo",
           "Value": "1"
         }
       ]
     }
   ],
   "Blame": null
 }