Cleanup after `server` and `build` commands.

We are currently not cleanuing up our `tmp/` directories after `build` and `server` are completed. This led to a 15 minute `rm -rf tmp/` session for me...

Screenshot of current behavior:

![screenshot](http://monosnap.com/image/DOfBma6wwoD3RlwmZ9jbwmsIaiAgJK.png)

Screenshot showing new behavior:

![Screenshot](http://monosnap.com/image/RhlH4ibzWXOxT2ztMmV5f1OChm1Yjf.png)