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..
No objections at all, but thanks for asking. I kinda suspected this would have to change anyway to get things to work with the dropbox script.