Use tripleo-admin user for minor updates

In Rocky we've moved to config-download, which also means ssh
administration via tripleo-admin user when running Ansible via
Mistral.

Using heat-admin no longer seems to work for freshly deployed Rocky
environments, we need tripleo-admin. For upgraded environments, the
assumption is that we'd create and authorize tripleo-admin user during
upgrade from Queens to Rocky, so using tripleo-admin for subsequent
minor update should be safe too.

Change-Id: If4f65d1001c23829fe3285493a6f18bc9af05a99
Closes-Bug: #1789220

tripleoclient/tests/v1/overcloud_update/test_overcloud_update.py

@@ -174,7 +174,7 @@ class TestOvercloudUpdateRun(fakes.TestOvercloudUpdateRun):
                     inventory_file=mock_open().read(),
                     playbook=book,
                     ansible_queue_name=constants.UPDATE_QUEUE,
-                    node_user='heat-admin',
+                    node_user='tripleo-admin',
                     tags='',
                     skip_tags=''
                 )
@@ -204,7 +204,7 @@ class TestOvercloudUpdateRun(fakes.TestOvercloudUpdateRun):
                     inventory_file=mock_open().read(),
                     playbook=book,
                     ansible_queue_name=constants.UPDATE_QUEUE,
-                    node_user='heat-admin',
+                    node_user='tripleo-admin',
                     tags='',
                     skip_tags=''
                 )

tripleoclient/v1/overcloud_update.py

@@ -128,7 +128,7 @@ class UpdateRun(command.Command):
         parser.add_argument("--ssh-user",
                             dest="ssh_user",
                             action="store",
-                            default="heat-admin",
+                            default="tripleo-admin",
                             help=_("The ssh user name for connecting to "
                                    "the overcloud nodes.")
                             )