rgw: translate swift request to s3 when forwarding

When forwarding a swift request to a different region, we
need to use the effective uri, and not just send the one
we got since we use S3 authentication for the forwarded
requests. This is achieved through a new using 'effective_uri'
param on the request info (which in swift ponts to the
plain bucket/object uri without the swift/v1 prefix(.
Also, rename the old req_state::effective_uri to relative_uri
in order to prevent confusion.

Signed-off-by: Yehuda Sadeh <yehuda@inktank.com>
rgw: swift, in create bucket set location_constraints

For swift we're setting the location constraint to be the
current region we're in when creating a bucket.

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