Improve error reporting in test suites

Before running each test case clear the thread local error
indicator. After running each test case, dispatch any error
that was reported

* tests/testutils.c: Fix error reporting in test suites

tests/testutils.c

@@ -124,8 +124,12 @@ virtTestRun(const char *title, int nloops, int (*body)(const void *data), const
 
         if (ts)
             GETTIMEOFDAY(&before);
+        virResetLastError();
         if ((ret = body(data)) != 0)
             break;
+        virErrorPtr err = virGetLastError();
+        if (err)
+            virDispatchError(NULL);
         if (ts)	{
             GETTIMEOFDAY(&after);
             ts[i] = DIFF_MSEC(&after, &before);