1092989: assume no uploads are in progress if upload working dir does not exist

Previously, pulp-admin would output an error to ~/.pulp/admin.log if "repo
uploads list"  was run without a repo upload working dir.

Instead, check for an exception if the repo upload working dir does not exist,
and assume no uploads are in progress if this is the case.

Also, general pep8 fixups on the two edited files.