Attach detach disk

* disk provider
   * added attach/detach
   * added whyrun support
   * better error handling to disk create/delete
   * cleaned up needed disk create arguments
   * new disk_attached? and disk_ready? functions
* other changes
   * changed default actions to metadata and tags
   * version bump and maintainer email
Does it make sense to allow "turbo mode" here?  https://github.com/chef-partners/google-compute-engine/blob/master/providers/instance.rb#L107