[system-tests][swarm] We need to switch gre to tun in systests for 8.0

[Vladimir Khlyunev]

Since we are not supporting gre deployment in 8.0 we should refactor all gre tests (switch it to tun);

List of affected tests (feel free to update it with missed tests):
fuelweb_test/tests/test_neutron: L86 entire class NeutronGreHa
fuelweb_test/tests/tests_strength/test_neutron.py: L137 entire class TestNeutronFailoverGRE
fuelweb_test/tests/tests_strength/test_image_based.py: L52
fuelweb_test/tests/test_offloading_types.py: L185
fuelweb_test/tests/test_pullrequest.py: L50 (should be completely removed?)
fuelweb_test/tests/tests_upgrade/test_upgrade.py: snapshot names

Affected Jenkins job
https://product-ci.infra.mirantis.net/view/8.0_swarm/job/8.0.system_test.ubuntu.rollback_neutron_gre
https://product-ci.infra.mirantis.net/view/8.0_swarm/job/8.0.system_test.ubuntu.ha_neutron_destructive_gre/

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/252507

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/252507
Committed: https://git.openstack.org/cgit/openstack/fuel-qa/commit/?id=0a61b2a16edef3acd2cb3971bff2bb99e9479bd1
Submitter: Jenkins
Branch: master

commit 0a61b2a16edef3acd2cb3971bff2bb99e9479bd1
Author: asledzinskiy <email address hidden>
Date: Wed Dec 2 18:33:47 2015 +0200

    Remove tests with 'gre' network

    - Remove 'gre' tests from tests_strength/test_neutron.py
    - Change 'gre' to 'tun' in test_image_based.py
    - Change 'gre' to 'tun' in test_pullrequest.py

    Change-Id: Ic1467e40be58782fed1ace51784b946c1d823153
    Closes-Bug: #1512285

[Fuel Devops McRobotson (fuel-devops-robot)]

Related fix proposed to branch: master
Change author: Artem Panchenko <email address hidden>
Review: https://review.fuel-infra.org/14477

[Tatyanka (tatyana-leontovich)]

All tests were switched except several one (we still need to test gre - according it available over api)

[Fuel Devops McRobotson (fuel-devops-robot)]

Change abandoned by Ivan Remizov <email address hidden> on branch: master
Review: https://review.fuel-infra.org/14477
Reason: This patch should be abandoned because it's too diverged with actual code and requires deep rework