Draft: simplify kube-job design / cleanup get-openstack-images
This MR covers rework, improvements and cleanups around kube-job, kube-cronjob and get-openstack-images job:
- heavily refactors kube-job
- the idea is that, since we've now move sylva-units to the sylva-system namespace, we don't need to have resources for kube-job units be in a kube-job namespace (Closes #1070)
- another idea is that we can introduce a unit template to avoid repetitions in the definition of units that rely on kube-job
- some similar/related simplifications where possible in kube-cronjob and the unit that uses it
- the get-openstack-images benefited from similar cleanups (and I ended up doing a bit more...)
Edited by Thomas Morin