Incorrect version of Sahara vanilla plugin in OSTF tests

[Evgeny Sikachev]

ENVIRONMENT: MOS 8.0

STEPS TO REPRODUCE:
1. Deploy env with Sahara
2. Run Sahara OSTF tests

EXPECTED RESULT:
Tests passed

ACTUAL RESULT:
NodeGroup cannot be created, because of "Vanilla has not supported version 2.7.1"

In MOS 8.0 uses Vanilla 2.7.1 instead 2.6.0. Need update Sahara OSTF tests for actual version of Vanilla plugin

[Evgeny Sikachev (esikachev)]

https://review.openstack.org/#/c/242009/

[Kristina Berezovskaia (kkuznetsova)]

Verify on:
VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "8.0"
  api: "1.0"
  build_number: "429"
  build_id: "429"
  fuel-nailgun_sha: "12b15b2351e250af41cc0b10d63a50c198fe77d8"
  python-fuelclient_sha: "4f234669cfe88a9406f4e438b1e1f74f1ef484a5"
  fuel-agent_sha: "df16d41cd7a9445cf82ad9fd8f0d53824711fcd8"
  fuel-nailgun-agent_sha: "92ebd5ade6fab60897761bfa084aefc320bff246"
  astute_sha: "c7ca63a49216744e0bfdfff5cb527556aad2e2a5"
  fuel-library_sha: "3eaf4f4a9b88b287a10cc19e9ce6a62298cc4013"
  fuel-ostf_sha: "214e794835acc7aa0c1c5de936e93696a90bb57a"
  fuel-mirror_sha: "b62f3cce5321fd570c6589bc2684eab994c3f3f2"
  fuelmenu_sha: "85de57080a18fda18e5325f06eaf654b1b931592"
  shotgun_sha: "63645dea384a37dde5c01d4f8905566978e5d906"
  network-checker_sha: "9f0ba4577915ce1e77f5dc9c639a5ef66ca45896"
  fuel-upgrade_sha: "616a7490ec7199f69759e97e42f9b97dfc87e85b"
  fuelmain_sha: "e8e36cff332644576d7853c80b8a53d5b955420a"

Test Sahara test for launching a simple Vanilla2 cluster PASSED