[#29] Fix Failing Test due to Unwanted Port Reuse

It looks like this test was failing because the kernel is reusing the same port for two different sockets within the same application (despite us not asking for this at all). In JDK 9+, we can control this via `StandardSocketOptions.SO_REUSEPORT`, but that option is not available in JDK 8. As a workaround, setting address reuse on the placeholder socket seems to prevent the subsequent socket from binding to the same port.

opendj-server/src/test/java/org/forgerock/opendj/server/setup/model/ListenerSettingsTestCase.java

@@ -22,6 +22,7 @@
  *
  *
  *      Copyright 2014 ForgeRock AS.
+ *      Portions Copyright 2019 Wren Security.
  */
 package org.forgerock.opendj.server.setup.model;
 
@@ -72,13 +73,23 @@ public void testGetDefault() {
     public void testGetFreePort() throws Exception {
         // Finds a free socket
         final InetSocketAddress isa = TestCaseUtils.findFreeSocketAddress();
-        // Bound the free socket
-        final int port = isa.getPort();
-        final ServerSocket boundSocket = new ServerSocket(port);
-        // Verify the new port number is different from the free socket and verify it's free.
-        final int newPort = ListenerSettings.getFreeSocketPort(port);
-        assertThat(newPort).isNotEqualTo(port);
-        assertTrue(Math.abs(newPort - port) % PORT_INCREMENT == 0);
+
+        // Bind the free socket
+        final int boundPort = isa.getPort();
+        final ServerSocket boundSocket = new ServerSocket();
+
+        // NOTE: This seems to work for JDK 8+; but, in JDK 9+, the next code line should switch to
+        // being the following instead (which is more precise):
+        //
+        // boundSocket.setOption(StandardSocketOptions.SO_REUSEPORT, false);
+        //
+        boundSocket.setReuseAddress(false);
+        boundSocket.bind(new InetSocketAddress(boundPort));
+
+        // Verify the new port number is different from the bound socket and verify it's free.
+        final int newPort = ListenerSettings.getFreeSocketPort(boundPort);
+        assertThat(newPort).isNotEqualTo(boundPort);
+        assertTrue(Math.abs(newPort - boundPort) % PORT_INCREMENT == 0);
 
         boundSocket.close();
     }