testing: fix cppcheck ClientTest::registerTests() warning

cppcheck warns that "factory" might get overwritten. Probably
never happened becaued registerTests() is only called once, but
let's fix it anyway.

test/ClientTest.cpp

@@ -6654,6 +6654,7 @@ private:
 
 void ClientTest::registerTests()
 {
+    freeFactory();
     factory = (void *)new ClientTestFactory(*this);
     CppUnit::TestFactoryRegistry::getRegistry().registerFactory((CppUnit::TestFactory *)factory);
 }
@@ -6665,15 +6666,20 @@ ClientTest::ClientTest(int serverSleepSec, const std::string &serverLog) :
 {
 }
 
-ClientTest::~ClientTest()
+void ClientTest::freeFactory()
 {
     if(factory) {
         CppUnit::TestFactoryRegistry::getRegistry().unregisterFactory((CppUnit::TestFactory *)factory);
         delete (CppUnit::TestFactory *)factory;
-        factory = 0;
+        factory = NULL;
     }
 }
 
+ClientTest::~ClientTest()
+{
+    freeFactory();
+}
+
 void ClientTest::registerCleanup(Cleanup_t cleanup)
 {
     cleanupSet.insert(cleanup);

test/ClientTest.h

@@ -435,6 +435,7 @@ class ClientTest : private boost::noncopyable {
      * registerTests() and remains valid until the client is deleted
      */
     void *factory;
+    void freeFactory();
 };
 
 /**