taskcluster
consider setting TASKCLUSTER_PROXY_URL to http://taskcluster in d2g
Currently generic-worker sets TASKCLUSTER_PROXY_URL to http://localhost:<TaskclusterProxyPort>.
In docker-worker it defaults to http://taskcluster (the proxy there runs in a neighboring docker container), and as a result existing tasks have come to expect that value. It should be feasible, at least when TaskclusterProxyPort is 80, to have http://taskcluster work inside docker. (It might be a bit trickier when the port is not 80, while using --net=host, but let's maybe not worry about that just yet.)
I suspect that /etc/hosts is not getting updated in fxci workers, but I believe an entry is added in community workers, so in community I believe it was working out of the box with our images. We should check. This may just be an overlooked requirement in our docs etc.
This isn't about the worker's /etc/hosts, it's not relevant here AFAICT, since we're running inside docker. It's about tests expecting that value for the env var.