Adds support for custom image formats in scenarios

[OpenStack Infra]

https://review.openstack.org/114759

Dear documentation bug triager. This bug was created here because we did not know how to map the project name "openstack/tempest" to a launchpad project name. This indicates that the notify_impact config needs tweaks. You can ask the OpenStack infra team (#openstack-infra on freenode) for help if you need to.

commit b7c1daaa7fde307f777309e9109f34a30c42149b
Author: Alessandro Pilotti <email address hidden>
Date: Sat Aug 16 14:24:13 2014 +0300

    Adds support for custom image formats in scenarios

    Scenario Tempest tests don't work on Hyper-V due to the missing
    support for VHD/VHDX image formats in the Tempest scenario comfiguration.

    The commits adds options to specify custom image disk and container
    formats, mantaining 'QCoW2' and 'bare' as the default options for
    backwards compatibility.

    Closes-bug: #1357691
    Co-Authored-By: Ionut Balutoiu <email address hidden>
    DocImpact

    Change-Id: I41c09d5a682cdb068b97b4bd1be3403ee7973c7c