Reserve Server Ports in integrationTests

Previously the build would look up a server port dynamically, but since
it closed the port immediately it may not be reserved by the time jetty
started up.

We now reserve the port and do not close it till just before Jetty starts.
While there is still a race condition, it is much smaller window of time
than it was previously.

samples/cas/sample/cassample.gradle

@@ -104,22 +104,26 @@ gradle.taskGraph.whenReady {graph ->
     }
     if(graph.hasTask(integrationTest)) {
         tasks.getByPath(':spring-security-samples-casserver:casServerOverlay').logLevel = 'ERROR'
-        jettyRunWar.additionalRuntimeJars += file("src/integration-test/resources")
+        jettyRunWar {
+            additionalRuntimeJars += file("src/integration-test/resources")
+            daemon = true
+        }
 
-        jettyRunWar.daemon = true
-        jettyRunWar.httpConnector.port = availablePort()
-        jettyRunWar.httpsConnector.port = jettyRunWar.httpConnector.confidentialPort = availablePort()
-        casServer.httpsConnector.port = availablePort()
+        [jettyRunWar.httpConnector,jettyRunWar.httpsConnector,casServer.httpsConnector]*.metaClass*.reservePort { taskToCloseSocket ->
+            def serverSocket = new ServerSocket(0)
+            delegate.metaClass.serverSocket = serverSocket
+            delegate.port = serverSocket.localPort
+            taskToCloseSocket.doFirst {
+                serverSocket.close()
+            }
+        }
+
+        [jettyRunWar.httpConnector,jettyRunWar.httpsConnector]*.reservePort(jettyRunWar)
+        jettyRunWar.httpConnector.confidentialPort = jettyRunWar.httpsConnector.port
+        casServer.httpsConnector.reservePort(casServer)
     }
 }
 
 def casServer() {
     tasks.getByPath(':spring-security-samples-casserver:casServer')
-}
-
-def availablePort() {
-    ServerSocket server = new ServerSocket(0)
-    int port = server.localPort
-    server.close()
-    port
-}
+}