Power sequencing of a multi-enclosure array

To ensure proper discovery in a multi-enclosure array, power on the expansion shelves first (DE120S, DE240S, DE600S) before powering on the attached controller. Wait about 2 minutes before powering on the controller enclosure. This allows enough time for the drives in the expansion shelves to power up before the controllers start discovery, which will prevent volumes being failed due to missing elements while expansion shelves are powering up.