qemu.test.cfg: Add cmd /c for windows disk write test

Add cmd /c to let the cmd session wait util the autoit scripts finished.
Otherwise it will return immediately after the autoit scripts start.
Also correct the script name.
Signed-off-by: NYiqiao Pu <ypu@redhat.com>

qemu/tests/cfg/win_disk_write.cfg

@@ -3,5 +3,5 @@
     only Windows
     type = win_disk_write
     drive_cache = writeback
-    crystal_install_cmd = D:\cystaldisk_install.exe
-    crystal_run_cmd = D:\run_cystalfdisk.exe
+    crystal_install_cmd = cmd /c D:\crystaldisk_install.exe
+    crystal_run_cmd = cmd /c D:\run_crystaldisk.exe