Expose lockutils opts to config generator

* Adds an opts module for the config generator to use.
* Makes the opts in lockutils private since we don't want consumers
  using them directly.
* Moves the options to an oslo_concurrency group with appropriate
  deprecated_group settings to keep existing configs working.

Change-Id: Ifdb4d99e27588e8a91d941c60b248ea526c06e0a