Add cascade delete option

[pbalogh-sa]

Signed-off-by: Peter Balogh p.balogh.sa@gmail.com

Q	A
Bug fix?	no
New feature?	yes
API breaks?	no
Deprecations?	no
Related tickets	fixes #X, partially #Y, mentioned in #Z
License	Apache 2.0

What's in this PR?

In the case of destroying a job, the pods aren't deleted. With this feature, we can set a cascade delete.

resource "k8s_manifest" "job" {
  content = "${data.template_file.job.rendered}"
  delete_cascade = true
}