If we set checkpoint-delay through command 'migrate-set-parameters',
It will not take effect until we finish last sleep chekpoint-delay,
That's will be offensive espeically when we want to change its value
from an extreme big one to a proper value.

Fix it by using timer to realize checkpoint-delay.
Signed-off-by: Nzhanghailiang <zhang.zhanghailiang@huawei.com>
Message-Id: <1484657864-21708-2-git-send-email-zhang.zhanghailiang@huawei.com>
Signed-off-by: NDr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: NDr. David Alan Gilbert <dgilbert@redhat.com>