intermitten unit test failure due to "too few arguments"

[Min Pae]

Intermitten unittest failure is being caused by the cue.cmd.manage
module adding required command line arguments such that given:

- Test A tests the cue.cmd.manage module
- Test B exercises code that attempts to parse config arguments
- Test A runs before Test B

Test B will always fail because it will not provide the required
arguments that were added by cue.cmd.manage when Test A was run.

The solution is to use a config fixture for unit tests. If the config
fixture provided all of the same interfaces as the global cfg.CONF
object, it could be used in place of the CONF object, but that is not
supported by the current version of oslo_config.