Fstrings are not supported in python3.5 which is in use on Xenial.
We don't claim to support Xenial, but this is an easy regression
to avoid.
Also, add test jobs for this role so that we get feedback before
copying it to the prod roles.
Also, add a xenial test job to exercise it since we still have
Xenial nodes available.
Change-Id: Ifc773aa688adb1a01cfe691b3bdca0b3086658cd
d6ae964f47