Add flag for UrlFetch (GoogleCloudPlatform#1507)

* Add flag for UrlFetch

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Author: averikitsch

appengine-java8/urlfetch/src/main/webapp/WEB-INF/appengine-web.xml

@@ -2,4 +2,7 @@
 <appengine-web-app xmlns="http://appengine.google.com/ns/1.0">
   <runtime>java8</runtime>
   <threadsafe>true</threadsafe>
+  <!-- Enable old appengine Java 7 behavior for Networking -->
+  <!-- For more info, see https://cloud.google.com/appengine/docs/standard/java/issue-requests -->
+  <url-stream-handler>urlfetch</url-stream-handler>
 </appengine-web-app>