Description of problem:
Cinder quotas break refresh when registering an Openstack cloud provider using Keystone v3 domains

[----] E, [2016-06-01T05:09:35.453581 #25175:1121988] ERROR -- : <Fog> excon.error     #<Excon::Errors::InternalServerError: Expected(200) <=> Actual(500 InternalServerError)
excon.error.response
  :body          => "{\"computeFault\": {\"message\": \"The server has either erred or is incapable of performing the requested operation.\", \"code\": 500}}"
  :cookies       => [
  ]
  :headers       => {
    "Content-Length"         => "128"
    "Content-Type"           => "application/json; charset=UTF-8"
    "Date"                   => "Wed, 01 Jun 2016 09:09:35 GMT"
    "X-Compute-Request-Id"   => "req-2de8c3a5-de00-4ec5-8ede-0549a50441da"
    "X-Openstack-Request-Id" => "req-2de8c3a5-de00-4ec5-8ede-0549a50441da"
  }
  :host          => "172.16.18.25"
  :local_address => "172.16.17.143"
  :local_port    => 57915
  :path          => "/v2/98f1116da56f487db1ea1ff156743c8e//os-quota-sets/98f1116da56f487db1ea1ff156743c8e"
  :port          => 8776
  :reason_phrase => "Internal Server Error"
  :remote_ip     => "172.16.18.25"
  :status        => 500
  :status_line   => "HTTP/1.1 500 Internal Server Error\r\n"
>

Version-Release number of selected component (if applicable):
5.6.0.8-rc1-nightly.20160531084619_1bff101

How reproducible:
100%

Steps to Reproduce:
1. Register Openstack cloud provider by using a Keystone v3 non default domain and the admin user of the domain
2. Refresh cloud provider

Actual results:
Refresh fails

Expected results:
Refresh completes fine.