issue0003: md5 & file size verfiy

1.verify file md5 when download end, if md5 is mismatch, task will be cancel
2.check the fileSize of input, if the fileSize is set, the download service will not query remote file size before download
3.fixbug: delete the work queue instead wait queue when download finish

Change-Id: I34101b452fd813626f21662630bb1887c687eee6