Merge pull request #185 from jaredbischof/master

Added external reference ID field to AWE workflow
Added code to retry a Shock download N times if it fails or the byte size or md5 checksum does not match what is in Shock, where N is a global variable in the script.  Also, added code to check file byte size before md5 checksum because it's quicker and if that fails we don't need to calculate the md5 checksum
Merge branch 'master' of github.com:MG-RAST/pipeline