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
Make lockutils main() a console entry point

This is more lib-ish than calling python -m on the module.

As part of this change, I also improved the unit tests for this code.
Before we weren't unsetting OSLO_LOCK_PATH before calling the main
function, so we had no way of knowing if it was being set correctly.

I also added a test case to verify return value propagation and
removed a private method that was never called.

Change-Id: I6c35b5409bf567767c5c71b9041dd7f7a012255d
Use ConfigFilter for opts

This will prevent them being registered on the global config object
and becoming available to consuming applications.

Change-Id: Ibddb876d18c6aefef9dca08cf5883d8bdca17925
bp graduate-oslo-concurrency