Filter out resources with no physical_resource_id

Filter out resources with no physical_resource_id.
Before we were ignoring those with:
https://github.com/Ladas/manageiq-providers-openstack/blob/d0799c4a5766650f2d3d149875c1b58f8a16040f/app/models/manageiq/providers/openstack/refresh_parser_common/orchestration_stacks.rb#L165

Without ignoring thise results in error :
[NoMethodError]: undefined method `ems_ref=' for nil:NilClass  Method:[block in method_missing]

app/models/manageiq/providers/openstack/inventory/parser/cloud_manager.rb

@@ -173,6 +173,8 @@ def orchestration_stack_resources(stack, stack_inventory_object)
     raw_resources.reject! { |r| r.physical_resource_id.nil? }
     raw_resources.each do |resource|
       uid = resource.physical_resource_id
+
+      next unless uid
       o = persister.orchestration_stacks_resources.find_or_build(uid)
       o.ems_ref = uid
       o.logical_resource = resource.logical_resource_id