win_virtio_driver_update_test.py:optimize changing cdrom process

replace boot up guest with new iso with change cdrom
Signed-off-by: NXiaoling Gao <xiagao@redhat.com>

qemu/tests/win_virtio_driver_update_test.py

 import logging
 
 from virttest import error_context
+from virttest import utils_misc
+from virttest import data_dir
+
 from qemu.tests import single_driver_install
 
 
@@ -23,11 +26,19 @@ def run(test, params, env):
     :param params: Dictionary with the test parameters
     :param env: Dictionary with test environment
     """
-    cdrom_virtio_downgrade = params.get("cdrom_virtio_downgrade")
-
     vm = env.get_vm(params["main_vm"])
     vm.verify_alive()
 
+    def change_virtio_media(cdrom_virtio):
+        """
+        change iso for virtio-win
+        :param cdrom_virtio: iso file
+        """
+        virtio_iso = utils_misc.get_path(data_dir.get_data_dir(),
+                                         cdrom_virtio)
+        logging.info("Changing virtio iso image to '%s'" % virtio_iso)
+        vm.change_media("drive_virtio", virtio_iso)
+
     if params.get("need_uninstall") == "yes":
         error_context.context("Uninstall virtio driver", logging.info)
         single_driver_install.run(test, params, env)
@@ -36,14 +47,14 @@ def run(test, params, env):
         error_context.context("Install virtio driver", logging.info)
     else:
         error_context.context("Downgrade virtio driver", logging.info)
-        new_params = params.copy()
-        new_params["cdrom_virtio"] = cdrom_virtio_downgrade
-        vm.create(params=new_params)
-        vm.verify_alive()
-        single_driver_install.run(test, new_params, env)
+        change_virtio_media(params["cdrom_virtio_downgrade"])
+        single_driver_install.run(test, params, env)
+        error_context.context("Reboot guest after downgrade virtio driver",
+                              logging.info)
+        vm.reboot()
         error_context.context("Upgrade virtio driver to original",
                               logging.info)
-    vm.create(params=params)
-    vm.verify_alive()
+
+    change_virtio_media(params["cdrom_virtio"])
     single_driver_install.run(test, params, env)
     vm.destroy()