single_driver_install.cfg:param "kill_after_test" is invalid now, using "kill_vm" instead

Signed-off-by: NYanan Fu <yfu@redhat.com>

qemu/tests/cfg/single_driver_install.cfg

@@ -2,7 +2,7 @@
     type = single_driver_install
     only Windows
     cdroms += " virtio winutils"
-    kill_after_test = yes
+    kill_vm = yes
     login_timeout = 360
     need_uninstall = no
     driver_install_timeout = 600

qemu/tests/cfg/win_virtio_driver_update_test.cfg

@@ -5,7 +5,7 @@
     monitors = qmp1
     cdroms += " virtio winutils"
     image_snapshot_image1 = yes
-    kill_after_test = yes
+    kill_vm = yes
     kill_vm_on_error = yes
     check_guest_bsod = yes
     login_timeout = 360