Use stable IDs for etcd, CoreDNS, and Ngnix dashboards

* Use unique dashboard ID so that multiple replicas of Grafana
serve dashboards with uniform paths
* Fix issue where refreshing a dashboard served by one replica
could show a 404 unless the request went to the same replica

addons/grafana/dashboards-coredns.yaml

@@ -1029,7 +1029,8 @@ data:
           "30d"
         ]
       },
-      "timezone": "browser",
+      "timezone": "",
       "title": "CoreDNS",
+      "uid": "2f3f749259235f58698ea949170d3bd5",
       "version": 0
     }

addons/grafana/dashboards-etcd.yaml

@@ -1224,7 +1224,8 @@ data:
           "30d"
         ]
       },
-      "timezone": "browser",
+      "timezone": "",
       "title": "etcd",
+      "uid": "c2f4e12cdf69feb95caa41a5a1b423d9",
       "version": 215
     }

addons/grafana/dashboards-nginx-ingress.yaml

@@ -1052,7 +1052,8 @@ data:
           "30d"
         ]
       },
-      "timezone": "browser",
+      "timezone": "",
       "title": "Nginx Ingress Controller",
+      "uid": "f4af03eca476c08ecf2b5cf15fd60168",
       "version": 0
     }