update failoverable error with 'ENOTFOUND'

Author: linglingye001

src/AzureAppConfigurationImpl.ts

@@ -835,6 +835,6 @@ function getValidFeatureFlagSelectors(selectors?: SettingSelector[]): SettingSel
 }
 
 function isFailoverableError(error: any): boolean {
-    return isRestError(error) && error.statusCode !== undefined &&
-        (error.statusCode === 401 || error.statusCode === 403 || error.statusCode === 408 || error.statusCode === 429 || error.statusCode >= 500);
+    return isRestError(error) && (error.code === 'ENOTFOUND' ||
+        (error.statusCode !== undefined && (error.statusCode === 401 || error.statusCode === 403 || error.statusCode === 408 || error.statusCode === 429 || error.statusCode >= 500)));
 }

src/requestTracing/constants.ts

@@ -43,7 +43,7 @@ export enum RequestType {
     STARTUP = "Startup",
     WATCH = "Watch"
 }
-export const FAILOVER_REQUEST_TAG = "Failover";
 
 // Tag names
+export const FAILOVER_REQUEST_TAG = "Failover";
 export const KEY_VAULT_CONFIGURED_TAG = "UsesKeyVault";