qemuTestDriverInit: fill driver with zeroes

In the commit aea47e48c4 we have fixed a single pointer within
driver structure. Since all callers pass statically allocated
driver on stack other pointers within driver may contain random
values too. Before touching it lets overwrite it with zeroes and
thus fix all dangling pointers.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

tests/testutilsqemu.c

@@ -555,11 +555,11 @@ int qemuTestCapsCacheInsert(virQEMUCapsCachePtr cache, const char *binary,
 
 int qemuTestDriverInit(virQEMUDriver *driver)
 {
+    memset(driver, 0, sizeof(*driver));
+
     if (virMutexInit(&driver->lock) < 0)
         return -1;
 
-    driver->securityManager = NULL;
-
     driver->config = virQEMUDriverConfigNew(false);
     if (!driver->config)
         goto error;