rgw: make APIs to work with tenants

rgw: make APIs to work with tenants

Previous commits introduced the tenant infrastructure such as
rgw_user, but did not allow anyone to access it productively.

Done:
 - radosgw-admin
 - bucket creation, listing, deletion with non-empty tenant
 - COPY
 - ACLs
 - Using colon for S3 with URL addressing

TODO:
 - Fix S3 remapping of DNS so that period turns into colon in buckets,
   possibly using typed endpoint domains, some assuming tenants
 - Have Swift authentication to set tenant into URL, then pick it there
 - Resolve leftover XXX

Signed-off-by: Pete Zaitcev <zaitcev@redhat.com>