Subclass Storages by provider

Now that a Storage record belongs_to an EMS we can subclass the storages
by provider.

db/migrate/20191210162908_add_type_to_storages.rb

@@ -0,0 +1,5 @@
+class AddTypeToStorages < ActiveRecord::Migration[5.1]
+  def change
+    add_column :storages, :type, :string
+  end
+end

db/migrate/20191210163518_subclass_storages.rb

@@ -0,0 +1,32 @@
+class SubclassStorages < ActiveRecord::Migration[5.1]
+  class ExtManagementSystem < ActiveRecord::Base
+    self.inheritance_column = :_type_disabled
+  end
+
+  class Storage < ActiveRecord::Base
+    include ActiveRecord::IdRegions
+
+    self.inheritance_column = :_type_disabled
+
+    belongs_to :ext_management_system, :foreign_key => :ems_id, :class_name => "SubclassStorages::ExtManagementSystem"
+  end
+
+  def up
+    [
+      'Microsoft',
+      'Redhat',
+      'Vmware',
+    ].each do |provider|
+      ems_class_name = "ManageIQ::Providers::#{provider}::InfraManager"
+      storage_class_name = "#{ems_class_name}::Storage"
+      Storage.in_my_region
+             .joins(:ext_management_system)
+             .where(:ext_management_systems => {:type => ems_class_name})
+             .update_all(:type => storage_class_name)
+    end
+  end
+
+  def down
+    Storage.in_my_region.update_all(:type => nil)
+  end
+end