Migrate tempest jobs to focal

As per victoria cycle testing runtime and community goal[1]
we need to migrate upstream CI/CD to Ubuntu Focal(20.04).

Most of the Tempest jobs will be migrate automatically once devstack
base job start running on Focal(Depends-On).

Few job like tempest-full-multinode and plugin sanity job needs to override
the nodeset. multinode job needs to run on Bionic till stable/ussuri and
on focal from master(victoria) onwards.

stable jobs testing stable branch needs to keep running on their supported
distro version which is bionic from stein till ussuri.

Keep 'tempest-integrated-compute' to run on bionic until
https://bugs.launchpad.net/qemu/+bug/1894804 is fixed.

Depends-On: https://review.opendev.org/#/c/731207/

[1] https://governance.openstack.org/tc/goals/selected/victoria/migrate-ci-cd-jobs-to-ubuntu-focal.html

Change-Id: I51fbd32a60c931d404e59e975049f7b01ed900dc
4 files changed