Restructure ig/env/agent/settings/disks

[jandubois]

Is your feature request related to a problem? Please describe.

Currently the disks entry includes a volume sub-structure, that does not really belong there. It can be shared between multiple entries (but must only be included in one of them, randomly), and it is not subject to the filters specified, as the volume is global to the pod.

Describe the solution you'd like

I think there should be a separate ig/env/agent/settings/volumes structure that just includes the volume definitions for the pod.

Additional context

See https://github.com/cloudfoundry-incubator/kubecf/blob/b161cd8c29ca44ce64f3cc18b4791a9f4fac9597/deploy/helm/kubecf/assets/operations/instance_groups/diego-cell.yaml#L69-L96 for an example how a volume that is shared by 4 mounts is grouped in with one of the mount definitions.

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/172030696

The labels on this github issue will be updated when the story is started.