Merge pull request #2285 from qingwangrh/1848937_add_backup_image_for_driver_load

Adding backup/restore image action for driver_load testing

qemu/tests/cfg/driver_load.cfg

@@ -3,6 +3,9 @@
     kill_vm_on_error = yes
     login_timeout = 240
     repeats = 1
+    Windows:
+        backup_image_before_testing = yes
+        restore_image_after_testing = yes
     variants:
         - with_nic:
             no e1000