Add octavia-v2-dsvm-scenario-centos-8

This patch adds a new non-voting scenario job to test against CentOS 8
amphora images. Until CentOS 8 controllers are supported in Devstack,
this job runs Ubuntu controllers.

Depends-On: https://review.opendev.org/#/c/697128/
Change-Id: Ia5cffced9d5af2de3a85b91be5358a15234f5e25
2 files changed