Improve the user lock config options help message
Improve the user lock config options help message

Adding more information about below config options.
- user_lockout_duration
- user_lockout_failure_attempts

Change-Id: I5565361e313ade284b8a17eda35a9229292e3ad8

masayukig/tempest,cisco-openstack/tempest,openstack/tempest,masayukig/tempest,cisco-openstack/tempest,openstack/tempest