Handle new subunit version 2 log files.
Handle new subunit version 2 log files.

* modules/jenkins/files/slave_scripts/run-tox.sh: Subunit v2 log files
written by testr will output to .testrepository/$id.2. If this file is
present copy it instead of .testrepository/$id as the subunit log.

Change-Id: I3b43aa2c267773ee9d51ca369f0236e8bf9d628d
Reviewed-on: https://review.openstack.org/26417
Reviewed-by: lifeless <a2625afd9a2a1367fa2df61966453044ff840158@robertcollins.net>
Reviewed-by: James E. Blair <e81a02a9d6405977f63a769d9f6ec8ed9d924325@inaugust.com>
Approved: Jeremy Stanley <98883b97e35b7bb1ac282bb863f2e9d917db0454@yuggoth.org>
Reviewed-by: Jeremy Stanley <98883b97e35b7bb1ac282bb863f2e9d917db0454@yuggoth.org>
Tested-by: Jenkins

open-switch/infra_puppet-jenkins,open-switch/infra_puppet-jenkins