issue0025-better-log-and-more-retry-times

1. when download failed, set retry time to 10
2. Write more info to log to help find failed problem

How to test:

1. write the full url(start with http:// or ftp://) you want to download to  test/download_urls
2. run

cd test
go test -run UrlsDownload -v

Change-Id: Ibaef5245ba001414f90a8fc7a96c4f4ec77210fe