Fix missing 'storages' association on Datacenter

When provisioning a Vm as a user that belongs to a group with a
belongs_to filter applying Rbac on storages fails due to a missing
virtual_has_many on the Datacenter base class.

app/models/ems_folder.rb

@@ -18,6 +18,7 @@ class EmsFolder < ApplicationRecord
   virtual_has_many :vms,               :uses => :all_relationships
   virtual_has_many :miq_templates,     :uses => :all_relationships
   virtual_has_many :hosts,             :uses => :all_relationships
+  virtual_has_many :storages,          :uses => :all_relationships
 
   virtual_attribute :folder_path, :string, :uses => :all_relationships
 

spec/models/miq_request_workflow_spec.rb

@@ -348,6 +348,23 @@
             expect(workflow.allowed_storages.map(&:id)).to eq([storage_2.id])
           end
         end
+
+        context "with a user with a belongs_to_filter" do
+          before do
+            group = workflow.requester.miq_groups.first
+            group.entitlement = Entitlement.new
+            group.entitlement.set_managed_filters([])
+            group.entitlement.set_belongsto_filters(["/belongsto/ExtManagementSystem|#{ems.name}/EmsFolder|Datacenters"])
+            group.save!
+          end
+
+          it "filters out storages" do
+            allow(workflow).to receive(:get_source_and_targets).and_return(:ems => workflow.ci_to_hash_struct(ems))
+            allow(workflow).to receive(:allowed_hosts_obj).and_return([host])
+
+            expect(workflow.allowed_storages.map(&:id)).to be_empty
+          end
+        end
       end
 
       context "with read-only storages" do