service flattening broke nova vnc proxy

The service flattening introduced in a recent commit [1] broke nova vnc proxy.

The error one gets is as follows:

2019-02-13 05:39:55 | Creating overcloud Heat stack
2019-02-13 05:39:55 | Error during stack creation: ERROR: UserParameterMissing: : resources.ControllerServiceChain<https://192.168.24.2:13808/v1/AUTH_b8268ca2f8804a35b2c1a80ea9fc003f/overcloud/common/services.yaml>.resources.ServiceChain<nested_stack>.resources.114<https://192.168.24.2:13808/v1/AUTH_b8268ca2f8804a35b2c1a80ea9fc003f/overcloud/deployment/nova/nova-vnc-proxy-container-puppet.yaml>: : The Parameter (StackUpdateType) was not provided.
2019-02-13 05:39:55 | Traceback (most recent call last):
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/common/context.py", line 410, in wrapped
2019-02-13 05:39:55 | return func(self, ctx, *args, **kwargs)
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/engine/service.py", line 849, in create_stack
2019-02-13 05:39:55 | parent_resource_name, template_id)
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/engine/service.py", line 753, in _parse_template_and_validate_stack
2019-02-13 05:39:55 | stack.validate()
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/osprofiler/profiler.py", line 160, in wrapper
2019-02-13 05:39:55 | result = f(*args, **kwargs)
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/engine/stack.py", line 897, in validate
2019-02-13 05:39:55 | result = res.validate()
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/engine/resources/template_resource.py", line 268, in validate
2019-02-13 05:39:55 | result = super(TemplateResource, self).validate()
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/engine/resources/stack_resource.py", line 66, in validate
2019-02-13 05:39:55 | self.validate_nested_stack()
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | File "/usr/lib/python2.7/site-packages/heat/engine/resources/stack_resource.py", line 82, in validate_nested_stack
2019-02-13 05:39:55 | ex, path=[self.stack.t.RESOURCES, path])
2019-02-13 05:39:55 |
2019-02-13 05:39:55 | StackValidationFailed: UserParameterMissing: resources.ControllerServiceChain<https://192.168.24.2:13808/v1/AUTH_b8268ca2f8804a35b2c1a80ea9fc003f/overcloud/common/services.yaml>.resources.ServiceChain<nested_stack>.resources.114<https://192.168.24.2:13808/v1/AUTH_b8268ca2f8804a35b2c1a80ea9fc003f/overcloud/deployment/nova/nova-vnc-proxy-container-puppet.yaml>: The Parameter (StackUpdateType) was not provided.

[1] https://review.openstack.org/#/c/632522/