docker-compose.dev.yml starts an extra container in which a dev/test
instance of the agent is run with
SHELLHUB_TENANT_ID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx. This
container runs in the host network and pid namespace, which is
necessary so that it can launch SSHD child shells on behalf of the host.

However, The host network environment varies from host to host and
depending on docker bridge configuration. The docker-compose file had
hardcoded the address of the gateway from the host's network as
http://172.17.0.1, with an implicit gateway port of 80.  This will
not work on hosts with different bridge configuration or
when SHELLHUB_HTTP_PORT is not 80.

Since the dev agent is on the host network, localhost works to refer to a
gateway running on the same host as the dev agent.  So the solution is to
use localhost:${SHELLHUB_HTTP_PORT}...