Cancel update action for stack is failed at the last moment

[Alexander Nagovitsyn]

NOTE -use enwiroment 1 controller + 1 compute with a small amount of RAM (max 8gb for node)

Using template https://github.com/Mirantis/mos-integration-tests/blob/master/mos_tests/heat/templates/heat_create_neutron_stack_template.yaml
With this param:
parameters:
  InstanceType:
    type: string
    default: m1.tiny
  ImageId:
    type: string
    default: TestVM
  network:
    type: string
    default: admin_internal_net

1) heat stack-update -f Template_file.yaml -P InstanceType=m1.medium test
2) wait ~30 s (roughly the time needed to update the medium flavor)
3)heat stack-cancel-update test
Result:
Rollback_Failed: NotFound: resources.Server: Instance 4ab52eb2-879c-4af4-9b49-9bb7947223c3 could not be found. (HTTP 404) (Request-ID: req-1adeb0f1-d83e-40a0-9244-663f860f283d)
ResourceInError: Went to status ERROR due to "Message: No valid host was found. There are not enough hosts available., Code: 500"