Drop "hide_auth" config value

This was never really used.
Drop allow_account_management

The old code resulted in to the (save) default anyway. I don't think we
want to parameterize this currently. Most (if not all) customers want to
use keystone-based auth. For that, swift auto-creates account DB
entries.
Drop "group" configurable

This never existed, the code in swift.common.util:drop_privileges asks
the Unix password database for the group of "user".
Clarify string for delayed_auth
Minor cleanup
Merge pull request #190 from vuntz/saschpe

Small cleanups