Add guest internal read/write checking for cases virsh.migrate_storage.*

[qiankehan]

Recently, fjin has find a bug: Bug 1978716 - Storage is not copied at all when do vm live migration with --copy-storage-inc
It should have been cause failures on case rhel.virsh.migrate_storage.default.copy_storage_inc. But it was passed.
The guest internal read/write checkpoint will help to catch the bug like that.