rgw: user has a tenant property

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: remove old cruft

We're not reusing objects anymore, no need for clear()

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: buckets within tenant namespace

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>