Make $node_name unique to avoid deleting wrong droplet on failed provision

So those 'useful' changes I made before ended up deleting my live server :'( The code `droplet_id=$(knife digital_ocean droplet list | grep deis-controller | awk '{print $1}')` didn't account for multiple servers with the name 'deis-controller' so it just deletes the first one it finds. Not good.

So, here's a fix to give each server a unique name by appending a random string to 'deis-controller'. This is tested and works.