Comment 2 for bug 1343385

Fixed by: https://gerrit.mirantis.com/#/c/19020/

Fix stack inconsistency after app deletion

To expose IP addresses of Instance in MuranoPL we place new entry to
outputs section in Heat template that reference corresponding
AWS::EC2::Instance resource. During clean-up stage, if some application
was deleted from environment, we remove corresponding AWS:EC2:Instance
resource, but reference in outputs section stays.
Stack with reference to resource that is not present in template is
invalid - environment deployment fails.
This change add code that removes references to OS::Nova::Server when
corresponding Instance is deleted.
Change-Id: I1c8b53db59939abd45595a8e619bc5ebe5e12646
Attention: this change fix issue that can break murano-ci gate
Closes-Bug: #1343385
Note: this is backport of https://review.openstack.org/#/c/105686/