Fix missing cell type

Because we are now creating new instances of dashboards when we create a
response, it's critical to copy every element of Dashboards from the
previous to the new instance.

We were not previously copying the Type field of cells, so this was
defaulting to the empty string zero value. This patch adds "Type" to the
tests and ensures that it's properly copied

server/cells.go

@@ -45,6 +45,7 @@ func newCellResponses(dID chronograf.DashboardID, dcells []chronograf.DashboardC
 		newCell.H = cell.H
 		newCell.Name = cell.Name
 		newCell.ID = cell.ID
+		newCell.Type = cell.Type
 
 		for _, lbl := range labels {
 			if axis, found := cell.Axes[lbl]; !found {

server/cells_test.go

@@ -105,6 +105,7 @@ func Test_Service_DashboardCells(t *testing.T) {
 					W:       4,
 					H:       4,
 					Name:    "CPU",
+					Type:    "bar",
 					Queries: []chronograf.DashboardQuery{},
 					Axes:    map[string]chronograf.Axis{},
 				},
@@ -117,6 +118,7 @@ func Test_Service_DashboardCells(t *testing.T) {
 					W:       4,
 					H:       4,
 					Name:    "CPU",
+					Type:    "bar",
 					Queries: []chronograf.DashboardQuery{},
 					Axes: map[string]chronograf.Axis{
 						"x": chronograf.Axis{