[System Tests] Need to add test to check connectivity after neutron agents migrations

[Andrey Sledzinskiy]

Test steps will be the next:
1. Create neutron gre cluster, 3 controllers, 2 compute, 1 cinder and deploy
 2. Create instance and assign floating ip to it
 3. Add collocation between l3-agent and dhcp-agent
 4. Create agents_migration snapshot
 5. 10 times revert snapshot agents_migration
 6. Migrate manually dhcp-agent and l3-agent
 7. Check ping to floating ip
 8. In case of failure increase number of failures
 9. Restart openvswitch-agent on node with l3 agent
 10. Ping floating ip again
 11. In case of success increase number of workarounds on 1
 12. In case of failure increase number of failed workarounds on 1

This test is only actual for 5.1.1 branch. On 6.0 we have multiple l3 agents and case will be different

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/5.1
Review: https://review.openstack.org/137316

[Bogdan Dobrelya (bogdando)]

related critical bug https://bugs.launchpad.net/fuel/+bug/1393771
We use this script to find out the repro rate for it

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/137316
Committed: https://git.openstack.org/cgit/stackforge/fuel-main/commit/?id=e8a5b9c19dbb0b91fe8c1b039e9fdd11d988fe98
Submitter: Jenkins
Branch: stable/5.1

commit e8a5b9c19dbb0b91fe8c1b039e9fdd11d988fe98
Author: asledzinskiy <email address hidden>
Date: Wed Nov 26 11:16:57 2014 +0200

    Add test to find out statistic of connectivity failures
    in case of neutron agents migration

    - Add test in which we manually migrate l3 and dhcp agent
    and then check instance connectivity
    - Add methods to work with neutron client to OpenstackActions class

    Change-Id: I7645962889d729dca84a72ae725b3c281ce497b2
    Closes-Bug: #1396522