Add header tests to check for min/max (or lack of max) client version
user
```ruby
# -*- coding: utf-8 -*-
#
# Author:: Douglas Triggs (<doug@getchef.com>)
# Copyright:: Copyright (c) 2014 Chef, Inc.

describe "Headers" do
  let (:request_url) { api_url("users") }
  let (:requestor) { platform.admin_user }

  context "Request Headers" do

    # Right, now, we're just checking header versions, this can also be a template
    # for future header tests if we need to test anything else.

    # TODO: add some more digits when Chef Client reaches version 999
    # I may be retired by then.
    let (:high_version_headers) { {"X-Chef-Version" => "999.0.0" } }
    let (:low_version_headers) { {"X-Chef-Version" => "9.0.1" } }

    it "Accepts High Version" do
      get(request_url, requestor, :headers => high_version_headers).should look_like({
          :status => 200
        })
    end

    it "Rejects Low Version" do
      get(request_url, requestor, :headers => low_version_headers).should look_like({
          :status => 400
        })
    end
  end # context "Request Headers"
end # describe "Headers"
```
assistant