+++ This bug was initially created as a clone of Bug #2006772 +++

Description of problem:
While trying to complete undercloud upgrade from RHOSP16.1.5 to RHOSP16.2 the deployment fails with the following error:
~~~
[  admin] TASK [Create /etc/openstack directory if it does not exist] ********************************************************
[  admin] fatal: [director -> undercloud]: UNREACHABLE! => {"changed": false, "msg": "Failed to connect to the host via ssh: ssh: Could not resolve hostname undercloud: Name or service not known", "unreachable": true}
[  admin] NO MORE HOSTS LEFT *************************************************************************************************
[  admin] PLAY RECAP *********************************************************************************************************
[  admin] director                   : ok=14   changed=0    unreachable=1    failed=0    skipped=0    rescued=0    ignored=0
[  admin] Exception: Post Upgrade failed

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Deployment Failed!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

ERROR openstack [  admin] Deployment failed.
ERROR tripleoclient.v1.undercloud.UpgradeUndercloud [  ]

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
An error has occured while deploying the Undercloud.
See the previous output for details about what went wrong.
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
~~~


Checking the undercloud upgrade tarball I can see this in the inventory:
~~~
Undercloud:
  hosts:
    director: {ansible_host: 192.168.24.1, canonical_hostname: director.localdomain,
      ctlplane_hostname: director.ctlplane.localdomain, ctlplane_ip: 192.168.24.1,
      deploy_server_id: a081cb61-5302-4134-9684-490d633392c6, external_hostname: director.external.localdomain,
      external_ip: 192.168.24.1}
~~~

So we can see that it's trying to target the "undercloud" hostname but my undercloud hostname is "director"

Updating "delegate_to: undercloud" to delegate_to: "{{ groups['Undercloud'][0] }}" I was able to pass this issue:

https://review.opendev.org/c/openstack/tripleo-heat-templates/+/810345

Version-Release number of selected component (if applicable):
openstack-tripleo-heat-templates-11.5.1-2.20210603174823.el8ost.9.noarch
Red Hat OpenStack Platform release 16.2.0 GA (Train)


How reproducible:
Every time

Steps to Reproduce:
1.Follow minor update guide
2.Once you get to openstack undercloud upgrade it will fail with the above message

Actual results:
Undercloud upgrade fails

Expected results:
Undercloud upgrade to complete sucessfully