testscript: add encode test and get video content from bee server

1. use psnr to test yamiencode
2. get video content from bee server
you can use unit_test.sh git://bee.sh.intel.com/git/media/bat_video_content to download video, and autotest  all the download file which is 2 level folder.
you can use unit_test.sh ./bat_video_content/  (with child folder) to test all the files.