title: Vagrant, error when running vagrant up --provider=docker
body: <p>I'm trying to test the new docker support in vagrant 1.6. I'm on windows and I've setup my vagrant file but when I run "vagrant up --provider=docker" I get the following:</p>
  
  <pre><code>Bringing machine 'default' up with 'docker' provider...
  ==&gt; default: Docker host is required. One will be created if necessary...
  default: Vagrant will now create or start a local VM to act as the Docker
  default: host. You'll see the output of the `vagrant up` for this VM below.
  default:
  default: Box 'mitchellh/boot2docker' could not be found. Attempting to find and install...
  default: Box Provider: virtualbox
  default: Box Version: &gt;= 0
  default: Loading metadata for box 'mitchellh/boot2docker'
  default: URL: https://vagrantcloud.com/mitchellh/boot2docker
  default: Adding box 'mitchellh/boot2docker' (v0.8.0) for provider: virtualbox
  default: Downloading: https://vagrantcloud.com/mitchellh/boot2docker/version/1/provider/virtualbox.box
  default: Progress: 100% (Rate: 2999k/s, Estimated time remaining: --:--:--)
  The executable 'bsdtar' Vagrant is trying to run was not
  found in the %PATH% variable. This is an error. Please verify
  this software is installed and on the path.
  </code></pre>