[Tails-dev] Heads up: upgrade your Vagrant build setup

Hi,

The Vagrant basebox has been updated, and apparently Vagrant won't
switch to it automatically. To completely delete the old builder VM and
basebox, please run these commands from Tails' Git root:

    rake vm:halt
    rake vm:destroy
    vagrant box remove tails-builder-amd64-jessie-20160226
    VOLS="$(virsh vol-list default | \
            grep -o "tails-builder-amd64-jessie-20160226\S*\.img" | \
            uniq)"
    for vol in ${VOLS}; do virsh vol-delete --pool default ${vol}; done

To get the new Vagrant basebox, make sure to checkout a recent `devel`
(or merge it into the branch you want to build), and then run `rake
build` or `rake vm:up` or whatever you prefer.

Cheers!