qemumonitortestutils: Resolve resource leaks found by Valgrind

When Valgrind runs the 'qemumonitorjsontest' it would claim that the
thread created is leaked. That's because the virThreadJoin won't get
called due to the 'running' flag being cleared.  In order to avoid that,
call virThreadJoin unconditionally at cleanup time.  Also noted that the
qemuMonitorTestWorker() didn't get the test mutex lock on the failure path.

The incoming and outgoing buffers allocated by qemuMonitorTestIO() and
qemuMonitorTestAddReponse() were never VIR_FREE()'d in qemuMonitorTestFree().

tests/qemumonitortestutils.c

@@ -308,6 +308,7 @@ static void qemuMonitorTestWorker(void *opaque)
         virMutexUnlock(&test->lock);
 
         if (virEventRunDefaultImpl() < 0) {
+            virMutexLock(&test->lock);
             test->quit = true;
             break;
         }
@@ -370,12 +371,14 @@ void qemuMonitorTestFree(qemuMonitorTestPtr test)
 
     virObjectUnref(test->vm);
 
-    if (test->running)
-        virThreadJoin(&test->thread);
+    virThreadJoin(&test->thread);
 
     if (timer != -1)
         virEventRemoveTimeout(timer);
 
+    VIR_FREE(test->incoming);
+    VIR_FREE(test->outgoing);
+
     for (i = 0 ; i < test->nitems ; i++)
         qemuMonitorTestItemFree(test->items[i]);
     VIR_FREE(test->items);