HTTPConnectionPool: Read timed out

[Andrew Kalach]

Description
===========
During 9.0RC2 Certification Testing Sutie run, the following error logs appeared when
executing tasks:

    NovaSecGroup.create_and_delete_secgroups
    http://paste.openstack.org/show/524307/

    NovaSecGroup.create_and_list_secgroups
    http://paste.openstack.org/show/524309/

Steps to reproduce
==================
Install Rally on masternode and run tasks "NovaSecGroup.create_and_delete_secgroups" and
"NovaSecGroup.create_and_list_secgroups":

1. cd /opt/stack
2. source .venv/bin/activate
3. rally task start /opt/stack/rally-scenarios/nova/create_and_delete_secgroups.yaml
4. rally task start /opt/stack/rally-scenarios/nova/create_and_list_secgroups.yaml

Expected result
===============
Task run without errors

Actual result
=============
Errors described above in logs

Environment
===========
Scale 200-node lab (ENV-10):
  3 controllers
  199 compute nodes
  20 ceph nodes
  DVR enabled
  XVLAN
Image RC2 build:
  fuel-9.0-mos-495-2016-06-16_18-18-00.iso

Diagnostic snapshot:
  http://mos-scale-share.mirantis.com/fuel-snapshot-2016-06-28_13-13-50.tar.gz