From community meeting on 04-June-2019 Ubuntu Xenial is the default
image for Airship projects, but a desire was voiced to also add support
for Ubuntu Bionic at the convenience of the contributors for each
project.
This patch:
1. Adds a new dockerfile specific to ubuntu:18.04 (bionic)
2. Updates gates to be specific about which ubuntu image is being
checked.
3. Add to .zuul.yaml checks/gates/post jobs for bionic
Change-Id: Ib10641656f48baffec5b03ec48bf864d67209289
bf2f3781fb