common: don't do special things for unprivileged daemons

We generally do want an admin socket and log, and people usually run these
as root.  This is more confusing than useful.

Fixes: #6334
Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #723 from ceph/wip-6334

common: don't do special things for unprivileged daemons

Reviewed-by: Greg Farnum <greg@inktank.com>