extra/vm: Scripts to set up a Virtual Machine with stb-tester installed

This uses "vagrant", a tool for provisioning virtual machines. See
`extra/vm/README.rst` for instructions.

The VM is missing configuration for LIRC, and the RedRat3 doesn't work;
see the "Status" section in `extra/vm/README.rst` for details.
extra/vm: Install 3.5 kernel

The RedRat3 USB infrared emitter doesn't send infrared signals properly
with the redrat3 driver in kernels < 3.3 (the Ubuntu 12.04 stock kernel
is 3.2).

See https://wiki.ubuntu.com/Kernel/LTSEnablementStack for details on
this "linux-generic-lts-quantal" package.