MXS-2326: Add hint cloning test case

The test checks that the steps taken to reproduce the bug no longer result
in a failure to route the query correctly.

maxscale-system-test/mxs2326_hint_clone.cpp

@@ -0,0 +1,29 @@
+/**
+ * MXS-2326: Routing hints aren't cloned in gwbuf_clone
+ */
+
+#include "testconnections.h"
+
+int main(int argc, char** argv)
+{
+    TestConnections test(argc, argv);
+    Connection c = test.maxscales->rwsplit();
+    test.expect(c.connect(), "Connection should work: %s", c.error());
+
+    std::string correct_id = c.field("SELECT @@server_id -- maxscale route to server server4");
+
+    test.tprintf("Executing session command");
+    test.expect(c.query("SET @a = 1"), "SET should work: %s", c.error());
+
+    test.tprintf("Forcing a reconnection to occur on the next query by blocking the server");
+    test.repl->block_node(3);
+    test.maxscales->wait_for_monitor();
+    test.repl->unblock_node(3);
+    test.maxscales->wait_for_monitor();
+
+    test.tprintf("Executing a query with a routing hint to a server that the session is not connected to");
+    test.expect(c.check("SELECT @@server_id -- maxscale route to server server4",
+                        correct_id), "Hint should be routed to the same server");
+
+    return test.global_result;
+}