Updated openstack/openstack
Project: openstack/oslo.concurrency  6c5f5bfb2bd552eaa85b850b46f3e5575c401a15

Improve lock_path help and documentation

Improve help string to state default value and that it's mandatory.
Document set_defaults function.

DocImpact: Document that the value needs to evaluate to a valid path.
So, either environment variable is set or option is set.

Change-Id: I481d2f8107476ba166a18bc56d3b4c1be5ff726f