rgw: setting rgw_swift_url_prefix = "/" doesn't work as expected
3 - minor
According to the RadosGW's documentation in Jewel:
``rgw swift url prefix`` :Description: The URL prefix for the Swift StorageURL that goes in front of the "/v1" part. This allows to run several Gateway instances on the same host. For compatibility, setting this configuration variable to empty causes the default "/swift" to be used. Use explicit prefix "/" to start StorageURL at the root.