Use Vagrant's "docker-provider" to run a Dockerfile on any host. Works around issues with the current hashicorp/boot2docker image.

Vagrantfile

Vagrant.configure(2) do |config|

  # Generate shared docker-host Vagrantfile
  # (the default hashicorp/boot2docker image doesn't work very well at the moment)
  env = Vagrant::Environment.new
  vf_path = env.data_dir.join("docker-virtualbox-host", "Vagrantfile")
  begin
    env.lock("docker-provider-virtualbox-hostvm") do
      vf_path.dirname.mkpath
      File.open(vf_path, 'w') do |file|
        file.write <<-EOF
          Vagrant.configure(2) do |config|
            config.vm.box = "dduportal/boot2docker"
            # make sure Docker starts before SSH
            config.vm.provision "shell", inline: <<-SCRIPT
              # make sure Docker starts before SSH
              sed -i \
                -e '/Launch Docker/,$!{/Configure SSHD/,/^$/{H;d;};}' \
                -e '/Launch Docker/,/^$/{/^$/g;}' \
                /opt/bootscript.sh
              # and make sure it is started now
              /etc/rc.d/docker
            SCRIPT
          end
        EOF
      end
    end
  rescue Vagrant::Errors::EnvironmentLockedError
    # Lock contention, just retry
    retry
  end

  # Spawn a Docker container, natively if possible, or with the help of a VM.
  config.vm.define :default do |box_config|
    box_config.vm.provider :docker do |d|
      d.build_dir = "."
      d.vagrant_vagrantfile = vf_path
      d.remains_running = false
    end
  end

end

There are three issues this works around:

1. The current hashicorp/boot2docker image has password-based authentication, which does't play very nicely with Vagrant, and it lacks VirtualBox filesystem sharing support. The fix for this was to use @dduportal's fork of boot2docker, which includes key-based authentication and the VirtualBox extensions.
2. The dduportal/boot2docker image sometimes has the Docker daemon start a few seconds after SSH comes online, so Vagrant jumps the gun and produces an error. The fix was to re-arrange the boot scripts in the image to start SSH after Docker.
3. There is no good way to specify a custom shared docker-host VM in a Vagrantfile, so I had to do a re-implement part of the code from the provider-docker plugin directly in the Vagrantfile.