Fix storage_controller to show custom buttons

Closes #996

It cannot rely on @lastaction == 'show_list' because it's always 'explorer'. Introduced in ManageIQ/manageiq#11793

app/controllers/storage_controller.rb

@@ -479,8 +479,9 @@ def rebuild_toolbars(record_showing, presenter)
     c_tb = build_toolbar(center_toolbar_filename) unless @in_a_form
     h_tb = build_toolbar('x_history_tb')
     v_tb = build_toolbar('x_gtl_view_tb') unless record_showing || (x_active_tree == :storage_pod_tree && x_node == 'root') || @in_a_form
+    cb_tb = build_toolbar(custom_toolbar_explorer)
 
-    presenter.reload_toolbars(:history => h_tb, :center => c_tb, :view => v_tb)
+    presenter.reload_toolbars(:history => h_tb, :center => c_tb, :view => v_tb, :custom => cb_tb)
     presenter.set_visibility(h_tb.present? || c_tb.present? || v_tb.present?, :toolbar)
     presenter[:record_id] = @record.try(:id)
 
@@ -524,6 +525,10 @@ def textual_group_list
   end
   helper_method :textual_group_list
 
+  def custom_toolbar_explorer
+     @record.present? ?  Mixins::CustomButtons::Result.new(:single) : Mixins::CustomButtons::Result.new(:list)
+  end
+
   menu_section :inf
   has_custom_buttons
 end