966202 - Change the config options to use the optional parsers.

This allows config options to be unset using the syntax
--max-downloads=""
Automatic commit of package [python-okaara] minor release [1.0.32-1].
Bumped required version of okaara
Merge pull request #489 from pulp/jdob-966202

966202 - Config options should use the parse_optional_* methods