Handle zones that are being deleted (#663)

This patch handles Zones that are being deleted. We don't want to allow new VMs to be created in zones that are being deleted.
- If VM deployment specifies a zone that is being deleted by SSO user, validation webhook will reject the creation.
- If VM deployment specifies a zone that is being deleted by admin, validation webhook will allow the creation.
- If VM deployment specifies a valid zone at create time, zone got deletionTimestamp later, still place it in the zone.
- For placement, filter out the to be deleted zones so we don't have it as a candidate.

pkg/providers/vsphere/placement/zone_placement.go

@@ -112,6 +112,10 @@ func getPlacementCandidates(
 			zones = append(zones, zone)
 		}
 		for _, zone := range zones {
+			// Filter out the zone that is to be deleted, so we don't have it as a candidate when doing placement.
+			if zonePlacement && !zone.DeletionTimestamp.IsZero() {
+				continue
+			}
 			rpMoIDs := zone.Spec.ManagedVMs.PoolMoIDs
 			if childRPName != "" {
 				childRPMoIDs := lookupChildRPs(vmCtx, vcClient, rpMoIDs, zone.Name, childRPName)