[OSTF] Add instance deletion as a separate step for each test

[Tatyanka]

In case of instance deletion failure we need to notify users about it, Deletion from teardown do not provide such possibility
So we need add instance deletion as a separate step for each test where instance is created.
If deletion step failed - provide to user descriptive information

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/67107

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/67107
Committed: https://git.openstack.org/cgit/stackforge/fuel-ostf/commit/?id=8c8390af44b8792bfbb35a6622be84175c37498a
Submitter: Jenkins
Branch: master

commit 8c8390af44b8792bfbb35a6622be84175c37498a
Author: AnastasiiaNaboikina <email address hidden>
Date: Thu Jan 16 12:08:13 2014 +0200

    Provide message when server not deleted

    Added exception raising when server was not deleted which
    leads to test failure upon instance deletion step.
    Added minor changes to tests.

    Closes-bug: 1262128

    Change-Id: I00325c989725ab7048590a4362cd5322ae1f7264

[Tatyanka (tatyana-leontovich)]

verify on 70 iso