Add accessors for physical chassis tree

This commit exposes database schema changes to rails application.

app/models/physical_chassis.rb

@@ -7,10 +7,18 @@ class PhysicalChassis < ApplicationRecord
   belongs_to :ext_management_system, :foreign_key => :ems_id, :inverse_of => :physical_chassis,
     :class_name => "ManageIQ::Providers::PhysicalInfraManager"
   belongs_to :physical_rack, :foreign_key => :physical_rack_id, :inverse_of => :physical_chassis
+  belongs_to :parent_physical_chassis,
+             :class_name => "PhysicalChassis",
+             :inverse_of => :child_physical_chassis
 
   has_many :event_streams, :inverse_of => :physical_chassis, :dependent => :nullify
   has_many :physical_servers, :dependent => :destroy, :inverse_of => :physical_chassis
   has_many :physical_storages, :dependent => :destroy, :inverse_of => :physical_chassis
+  has_many :child_physical_chassis,
+           :class_name  => "PhysicalChassis",
+           :dependent   => :destroy,
+           :foreign_key => :parent_physical_chassis_id,
+           :inverse_of  => :parent_physical_chassis
 
   has_one :computer_system, :as => :managed_entity, :dependent => :destroy, :inverse_of => false
   has_one :hardware, :through => :computer_system