[system-tests] utils.timestat uses wrong variable 'traceback' to get 'format_exc()'

[Dennis Dmitriev]

Reproduced on CI: https://product-ci.infra.mirantis.net/job/7.0.system_test.ubuntu.thread_1/93/testReport/%28root%29/ha_one_controller_neutron_warm_restart/ha_one_controller_neutron_warm_restart/

System test 'ha_one_controller_neutron_warm_restart' was failed because of no space left on srv71-bud.infra.mirantis.net.

When the system test was trying to store the data about the time that consumed by the test, 'utils.timestat' was also failed, but there appeared a mistake in error handling:

  File "/home/jenkins/workspace/7.0.system_test.ubuntu.thread_1/fuelweb_test/helpers/utils.py", line 255, in __exit__
    " {1}".format(yaml_path, traceback.format_exc()))
AttributeError: 'traceback' object has no attribute 'format_exc'

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/231063

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/231063
Committed: https://git.openstack.org/cgit/stackforge/fuel-qa/commit/?id=cea127f5dc4aa1d2721774df04d10e183a8f1fdc
Submitter: Jenkins
Branch: master

commit cea127f5dc4aa1d2721774df04d10e183a8f1fdc
Author: Dmitry Tyzhnenko <email address hidden>
Date: Mon Oct 5 18:46:03 2015 +0300

    Fix using global variable in function

    Method used traceback param, when package import traceback module

    Change-Id: I1478ff933b3b2ae1fb4650230f4eca0da3c3e3b0
    Closes-bug: #1495438