Vagrant support, optional build firmware w/ image builder, update dev dependencies.

With this pull request we aim to make getting started with OpenWireless dead simple. To achieve this we have:

* Added a Vagrantfile to build a virtual machine to do development in.
* Add support for building the firmware with ImageBuilder (building from source in a virtual machine is took 3hrs+), building with image builder from cold takes about 8min, and with artifacts cached takes about 3.5min)
* Add xvfb/firefox to run selenium tests inside virtual machine.

We re-used the ```install-dev-dependencies.sh``` to provision the virtual machine to get consistency between folks running with and without the VM.

Each commit message elaborates on why it was required.
s/DIPLAY/DISPLAY ?  set -o nounset will catch these types of errors.