Use a single request to delete all pods

[isala404]

Currently, the reconciler cleanup lists all resources related to a flowtest and deletes them one at a time. The k8s api supports deleting a collection of resources by the labels. This is much more efficient and reduces the opportunity for errors.

The k8s api support deleting multiple pods with a single request. Is the functionality exposed with the reconciler?

Originally posted by @paynejacob in #11 (comment)