Update Server Class to accommodate different chef servers.
Update Server Class to accommodate different chef servers.

  - Introduce a new attribute 'chef_server_url'
  - If not passed in, the attribute will be set to the correct proxy
    server url that allows access to the chef12 server that resides in
    the internal VPC.
  - Also need to account for the variance in the
    'validation_client_name' within the 'client.rb' file.  Make sure
    that if we're using the legacy chef11 server that it gets set
    correctly.
  - Add the environment in the 'client.rb' file.  For now using the
    'environment' attribute in the Server Class.

hudl/Tyr