revert use of stestr in stable/pike

[Corey Bryant]

The following commit changed dependencies of nova in the stable/pike branch and switched it to use stestr. There aren't any other projects (as far as I can tell) that use stestr in pike. This causes issues, for example, the Ubuntu cloud archive for pike doesn't have stestr. If possible I think this should be reverted.

commit 5939ae995fdeb2746346ebd81ce223e4fe891c85
Date: Thu Jul 5 16:09:17 2018 -0400

    Backport tox.ini to switch to stestr

    The pike branch was still using ostestr (instead of stestr) which makes
    running tests significantly different from queens or master. To make
    things behave the same way this commit backports most of the tox.ini
    from queens so that pike will behave the same way for running tests.
    This does not use the standard backport mechanism because it involves a
    lot of different commits over time. It's also not a functional change
    for nova itself, so the proper procedure is less important here.

    Change-Id: Ie207afaf8defabc1d1eb9332f43a9753a00f784d

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/pike
Review: https://review.openstack.org/621227

[OpenStack Infra (hudson-openstack)]

Change abandoned by Corey Bryant (<email address hidden>) on branch: stable/pike
Review: https://review.openstack.org/621227

[Sahid Orentino (sahid-ferdjaoui)]

The patch which reverts the problematic change in Nova has been released in our packages for version 2:16.1.6-0ubuntu1~cloud0 [0]. Let's mark this bug has Fix Released [1].

For upstream Nova, the community are against the revert, it should probably be marked as won't fix.

[0] https://git.launchpad.net/~ubuntu-server-dev/ubuntu/+source/nova/commit/?h=stable/pike&id=f42d697d606bd1ceff54cce665fe80641956f932
[1] https://git.launchpad.net/~ubuntu-server-dev/ubuntu/+source/nova/commit/?h=stable/pike&id=21f71d906812a80ab3d1d96d22b04cf5744ed35c