Print errors from delete-organization
Skip unknown usernames rather than print "<unknown>".

Not sure what the original motivation for printing <unknown> was (it
shouldn't ever come up in normal operation, only if something weird
happens like we manually unset a user's username in the database). But
it's now rather inconvenient because we don't yet clean up deleted
organizations from a site, so you would see <unknown> for every
authorized organization that has been deleted. While we should
eventually clean up deleted organizations from a site's
"authorized_orgs" field, for now this will clean up the output of this
command.
Add guards against `proc` not existing in selftest
More organizations selftest