Improve retire_worker fallback by finding deployments name instead of pod name

[RossmacD]

Fallback to finding deployments rather than worker for deletion, as otherwise the pod can have the incorrect name, leading to workers not scaling down in adaptive mode.

Believe this was part of the issue on #910

[briceruzand]

Thanks @RossmacD , it looks like my trouble #855 (comment) (404 on deployments, because using pods name instead of deployments name)
I will try this fix on next release.