refactor: use existing docker ApiClient instance instead of creating a new one

[aaraney]

Use existing docker ApiClient instance instead of creating a new one.

scheduler tests were failing using docker desktop. see docker/docker-py#3198 and docker/docker-py#3219 for more detail. the gist is docker creates a context for docker desktop that uses a separate, non-default unix socket. for docker-py to play nicely with docker desktop, you must set DOCKER_HOST to the appropriate unix socket. You can locate the appropriate socket addr using: docker context inspect $(docker context show) | awk -F '"' '/"Host"/ {print $4}'.

dmod.scheduler -- 0.10.2

Changes

• use existing docker ApiClient instance instead of creating a new one