Add ChefSpec matcher

Adds a simple ChefSpec matcher, which allows for tests like this:

<pre>
  expect(runner).to create_certificate_manage('www.example.com').with(
    cert_path: '/path/to/certs',
    owner: 'username',
    group: 'groupname',
    key_file: "www.example.com.key",
    cert_file: "www.example.com.combined.crt",
    create_subfolders: false,
    nginx_cert: true
  )
</pre>