add fallback syntax for serverspec tests

[chris-rock]

This PR adds the ability to run plain Serverspec tests for IIS:

describe iis_website('Default Website') do
  it{ should exist }
  it{ should be_running }
  it{ should be_in_app_pool('Default App Pool') }
end

See http://serverspec.org/resource_types.html#iis_website

[vjeffrey]

👍