Vagrant support

This PR introduces Vagrant support. It's main benefits:

* simplifies finding/downloading/running the right OS. just have to run `vagrant up`
* removes entirely the need for `run_remote.sh`, which was somewhat duplicated with `run_local.sh`
* removes the need to SSH/SCP files to/from remote servers - build artifacts simply show up in the `output` directory at the repository root
* can run the same build in parallel on multiple vms

I have tested the builds on 10.04, 12.04, and 14.04 and they all work as expected. I have *not* tested or modified the Dropbox script.

Hope you find it useful..
This step is really hacky as you have to log in to Digital Ocean to find the right IP. Still trying to come up with an automated solution.