[Bug] Exception during exception in docker addons for volume removal

[frankcorneliusmartin]

Describe the bug

I got the following exception when stopping the v6 demo network:

  File "/Users/frankmartin/Repositories/vantage6/vantage6-common/vantage6/common/docker/addons.py", line 304, in delete_volume_if_exists
    log.warning("Could not delete volume %s", volume.name)
UnboundLocalError: local variable 'volume' referenced before assignment

Then I found that there is a bug in the docker add on:

vantage6/vantage6-common/vantage6/common/docker/addons.py

Lines 299 to 304 in 455a4c8

	try:
	volume = client.volumes.get(volume_name)
	if volume:
	volume.remove()
	except (docker.errors.NotFound, docker.errors.APIError):
	log.warning("Could not delete volume %s", volume.name)

Expected behavior
Make the exception handling independent of the retrieval of the volume name by using volume_name instead of volume.name