Description of problem:
Running FFU from OSP10 -> OSP13
When deployed overcloud, specified the stack name to be something different. 

Version-Release number of selected component (if applicable):
OSP10 -> OSP13

How reproducible:
every time

Steps to Reproduce:
1. Deploy OSP10 with --stack different_name
2. Perform FFU upgrade to OSP13 with openstack overcloud ffwd-upgrade run
3.

Actual results:
(undercloud) [stack@undercloud ~]$ openstack overcloud ffwd-upgrade run
Started Mistral Workflow tripleo.package_update.v1.update_nodes. Execution ID: 46caaa3b-bf7f-4d7b-96be-73cab0ddedb7
Waiting for messages on queue 'ffwdupgrade' with no timeout.
[u'Using /tmp/ansible-mistral-actionW8vHZ6/ansible.cfg as config file',
u' [WARNING]: Skipping unexpected key (hostvars) in group (_meta), only "vars",',
u'"children" and "hosts" are valid',
u' [WARNING]: Could not match supplied host pattern, ignoring: overcloud',
u'',
u'PLAY [overcloud] ***************************************************************',
u'skipping: no hosts matched',
u'',
u'PLAY RECAP *********************************************************************',
u'']
'headers'

Expected results:
things should start upgrading

Additional info:
There is a workaround:
tripleo-ansible-inventory --stack chrisj-ffu --static-yaml-inventory overcloud.yml
openstack overcloud ffwd-upgrade run --static-inventory overcloud.yml