Fix H233 in sphinx config

This is being flagged in local flake8 runs.

Change-Id: I99f05996711b3851811940ad5741e96d5ae61ed6
Run cfg.CONF.reset() on test cleanup

This means clear_override and clear_default do not
need to be called explicitly for each set_override and set_default
call.

This also fixes any potential test execution order issues
where an option has been set without being cleared at all.

Change-Id: Ic40c3be10b32eb3011bc0733cee9c1faaf8f1240
Fixes-Bug: #1221476
Merge "Fix H233 in sphinx config"
Merge "Run cfg.CONF.reset() on test cleanup"