At the moment it is very difficult to pull images from a private
registry that hasn't been configured on Kubernetes nodes as there
is no way to specify imagePullSecrets on pods.
This change introduces a snippet that can return a set of image
pull secrets using either a default or a per pod value. It also
adds this new snippet to the manifests for standard job types.
Change-Id: I710e1feffdf837627b80bc14320751f743e048cb
9d7baa9aa8