Add `origin master` to git pull for download-cache
Add `origin master` to git pull for download-cache

When building my 12.04 Vagrant box, it was not pulling the
bookie-download-cache repo. Specifying the remote and branch in the
command fixed it.

teodesson/Bookie,charany1/Bookie,adamlincoln/Bookie,skmezanul/Bookie,skmezanul/Bookie,wangjun/Bookie,wangjun/Bookie,skmezanul/Bookie,GreenLunar/Bookie,charany1/Bookie,GreenLunar/Bookie,adamlincoln/Bookie,bookieio/Bookie,bookieio/Bookie,skmezanul/Bookie,wangjun/Bookie,teodesson/Bookie,adamlincoln/Bookie,charany1/Bookie,adamlincoln/Bookie,GreenLunar/Bookie,GreenLunar/Bookie,teodesson/Bookie,bookieio/Bookie,teodesson/Bookie,bookieio/Bookie,wangjun/Bookie