[tempest] Sometimes apache-rgw interconnection returns 503

Detailed bug description:
tempest.api.image.v1.test_images.CreateRegisterImagesTest.test_register_http_image

Configuration:
    ISO: 9.0 mos iso #400
  Settings:
  Compute - QEMU.
  Network - Neutron with VLAN segmentation.
  Storage Backends - Ceph RBD for volumes (Cinder), Ceph RBD for ephemeral volumes (Nova), Ceph RBD for images (Glance), Ceph RadosGW for objects (Swift API)
  Additional services - Install Sahara

  In tab Settings->Compute check Nova quotas
  In tab Settings->OpenStack Services check enable Install Ceilometer and Aodh
  In tab Networks->Other check enable Neutron DVR

  Nodes: controller, compute, ceph-osd, Telemetry - MongoDB

Steps to reproduce:
    1. Deploy ISO in configuration see (Detailed bug description)
    2. Navigate to controller node
    3. Install git (use apt-get install git)
    4. Clone script to deploy rally + tempest
       # git clone https://github.com/obutenko/mos-rally-verify.git
    5. Navigate to the https://github.com/obutenko/mos-rally-verify
    6. Execute necessary steps to deploy tempest
    7. Tun test in debug mode
        #rally --debug verify start --regex tempest.api.image.v1.test_images.CreateRegisterImagesTest.test_register_http_image

Expected results:
Test is passed

Actual result:
Test is Failed
(see comments)

Reproducibility:
See attachment

Workaround:
Re-run test-case :)

Impact:
---

Related bug:
https://bugs.launchpad.net/mos/+bug/1585981

Description of the environment:
See (Detailed bug description)

Additional information:

On node-1 in HAproxy log:
2016-06-02T00:45:26.585959+00:00 node-1 haproxy[10915]: 10.109.1.3:44529 [02/Jun/2016:00:45:11.590] object-storage object-storage/node-2 6/0/1/10012/14994 503 473 - - SD-- 172/1/0/0/0 0/0 "PUT /swift/v1/glance/0c988f35-8ffc-437e-9396-4f11b41965ca HTTP/1.1"

On node-2 in Apache’s log:
10.109.1.3 - - [02/Jun/2016:00:45:11 +0000] "PUT /swift/v1/glance/0c988f35-8ffc-437e-9396-4f11b41965ca HTTP/1.1" 503 299 "-" "python-swiftclient-3.0.0"