## description

removing one server and updating the stack causes re-creation of all servers (possibly related to https://bugs.launchpad.net/heat/+bug/1671592 and https://review.openstack.org/#/c/452947/2/heat/engine/resources/stack_resource.py )

## my stack

$ nova list
host-0.example.com  192.168.0.5
host-1.example.com  192.168.0.6

hosts are

  - in a OS::Heat::ResourceGroup
  - in a ServerGroup with an anti-affinity policy

## reproduce

Delete one node
$ nova delete host-0.example.com
$ nova list
host-1.example.com

Stack check correctly detects the missing node (see paste)
$ heat action-check mystack

Run stack-update to recover the missing node
$ heat stack-update -x mystack


## I expect

The stack to be recovered to the original state

## Instead

Two more nodes are created, one with a conflicting name (the previously existing one).

$ nova list
host-1.example.com 192.168.0.6
host-0.example.com 192.168.0.11
host-1.example.com 192.168.0.12


## Pastes
2017-06-08 07:59:10Z [shift.openshift_infra_nodes.1]: CHECK_COMPLETE  Stack CHECK completed successfully. 'CHECK' not fully supported (see resources)  # SoftwareConfig & co
2017-06-08 07:59:10Z [shift.openshift_infra_nodes.1]: CHECK_COMPLETE  state changed
2017-06-08 07:59:10Z [shift.openshift_infra_nodes.0]: CHECK_FAILED  ['NotFound: resources[0].resources.root_volume: Volume 96187160-3c71-47de-98c9-2e3693e90003 could not be found. (HTTP 404) (Request-ID: req-696f3b71-1a4e-4984-a7cb-9d29b31157ad)']. 'CHECK' not fully supported (see resources)
2017-06-08 07:59:10Z [shift.openshift_infra_nodes]: CHECK_FAILED  Resource CHECK failed: ["['NotFound: resources[0].resources.root_volume: Volume 96187160-3c71-47de-98c9-2e3693e90003 could not be found. (HTTP 404) (Request-ID: req-696f3b71-1a4e-4984-a7cb-9d29b31157ad)']. 'CHECK' not fully supported (see resources)"]. 'C
2017-06-08 07:59:11Z [shift.openshift_infra_nodes]: CHECK_FAILED  ["['NotFound: resources.openshift_infra_nodes.resources[0].resources.root_volume: Volume 96187160-3c71-47de-98c9-2e3693e90003 could not be found. (HTTP 404) (Request-ID: req-696f3b71-1a4e-4984-a7cb-9d29b31157ad)']. 'CHECK' not fully supported (see resourc
2017-06-08 07:59:19Z [shift]: CHECK_FAILED  Resource CHECK failed: ['["[\'NotFound: resources.openshift_infra_nodes.resources[0].resources.root_volume: Volume 96187160-3c71-47de-98c9-2e3693e90003 could not be found. (HTTP 404) (Request-ID: req-696f3b71-1a4e-4984-a7cb-9d29b31157ad)\']. \'CHECK\' not