Upgrades, wrong error if there is no running nailgun

[Evgeniy L]

1. install 5.0
2. nailgun container was not running for some reasons (e.g. it happens if user didn't succeed to upgrade from the first time and then he wants to try again)
3. run upgrade to 5.1

Expected result:
User sees the message which is related to nailgun which is not running.

Actual result:
User sees the wrong message about died docker, in fact docker is up and running.

VERSION:
  feature_groups:
    - mirantis
  production: "docker"
  release: "5.1"
  api: "1.0"
  build_number: "503"
  build_id: "2014-09-08_00-01-11"
  astute_sha: "b622d9b36dbdd1e03b282b9ee5b7435ba649e711"
  fuellib_sha: "36ae367f521b1352b6303c6bddbe6a44519704f5"
  ostf_sha: "f7b5d9d0d1cfaba5f1fe1e2c634493e92bce11db"
  nailgun_sha: "c1ec85c185d3be1bd6c97cf1a821d1e020253a23"
  fuelmain_sha: "9978b759c7bdefff887e2ffb39588ef616b88517"

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/119788

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/119788
Committed: https://git.openstack.org/cgit/stackforge/fuel-web/commit/?id=d97c8f5e4cc42f8e179ff76cee296f6193a55f7c
Submitter: Jenkins
Branch: master

commit d97c8f5e4cc42f8e179ff76cee296f6193a55f7c
Author: Evgeniy L <email address hidden>
Date: Mon Sep 8 19:21:07 2014 +0400

    Upgrades, show appropriate error if nailgun isn't running

    Show a message to user for what to do if nailgun isn't
    running when user starts the upgrade.

    Change-Id: Iaabd281c43369884192fc34c85a293b70a9052ac
    Closes-bug: #1366848