Migrate to the latest Ubuntu LTS release 18.04 aka Bionic. See [0] for
the big picture.
Also test running tox jobs on Bionic.
[0] https://etherpad.openstack.org/p/devstack-bionic
Change-Id: I96e7b8d17bc1e92716c04fdcf362c2adb08a2212
With the current increase of zuul jobs and
service testing, is easier to maintain and
control what changes are done in different files.
Ideally jobs.yaml would be split into multiple files,
in example per distro, install type, aio or multinode,
etc
Change-Id: I78d3f1f00f96ef3042e94bba6b19e61d7fff4203