COLO: fix setting checkpoint-delay not working properly

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: zhanghailiang <zhang.zhanghailiang@huawei.com>
Message-Id: <1484657864-21708-2-git-send-email-zhang.zhanghailiang@huawei.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
