update CheckNameAvailability resource extra location in its route (#3004)

Author: juniwang

specification/signalr/resource-manager/Microsoft.SignalRService/preview/2018-03-01-preview/examples/CheckNameAvailability.json

@@ -1,5 +1,6 @@
 {
   "parameters": {
+    "location": "eastus",
     "parameters": {
       "type": "Microsoft.SignalRService/SignalR",
       "name": "my-signalr-service"

specification/signalr/resource-manager/Microsoft.SignalRService/preview/2018-03-01-preview/signalr.json

@@ -46,14 +46,21 @@
               }
           }
       },
-      "/subscriptions/{subscriptionId}/providers/Microsoft.SignalRService/checkNameAvailability": {
+      "/subscriptions/{subscriptionId}/providers/Microsoft.SignalRService/locations/{location}/checkNameAvailability": {
           "post": {
               "tags": [
                   "SignalR"
               ],
               "description": "Checks that the SignalR name is valid and is not already in use.",
               "operationId": "SignalR_CheckNameAvailability",
               "parameters": [
+                    {
+                        "name": "location",
+                        "in": "path",
+                        "description": "the region",
+                        "required": true,
+                        "type": "string"
+                    },
                   {
                       "name": "parameters",
                       "in": "body",
@@ -844,7 +851,10 @@
           "in": "query",
           "description": "Client Api Version.",
           "required": true,
-          "type": "string"
+          "type": "string",
+          "enum": [
+            "2018-03-01-preview"
+          ]
       },
       "SubscriptionIdParameter": {
           "name": "subscriptionId",