Deploy recipe: prune branches (#1664)

while I was in here added app name to the commands so we can see
in the chef log.  Helpful for debugging.
Add app name to collectstatic cmd for logging (#1664)
declutter chef output by saving away collectstatic (#1677)
Merge pull request #1678 from Stanford-Online/sef-1664-deploy-remote-prune

Sprint 28 chef nits: deploy pruning, collectstatic output Sef 1664 deploy remote prune