Fix secondary (overcloud) subnode indexes

Historically, as of Iaf43023db700d875d3569ed811069454d863cba8 we're
used to build the multinode inventory starting with subnode-2.
That's because nodepool originally was assuming subnode-1 is for
primary/undercloud. Later on there had been added the corresponding
primary/secondary groups with the pass-throw numeration starting from
0.

The old numeration scheme now breaks multi-node jobs deployed with the
new CI reproducer. Let's switch the indexing back to + 1.

Change-Id: I16e6e33179d5df9ddc93bae9046ea76ec337e0bd
Signed-off-by: Bogdan Dobrelya <bdobreli@redhat.com>

roles/tripleo-inventory/tasks/inventory.yml

@@ -47,7 +47,7 @@
     - name: Add subnode to ansible inventory
       with_indexed_items: '{{ nodes.stdout_lines | default([]) }}'
       add_host:
-        name: 'subnode-{{ item.0 + 2 }}'
+        name: 'subnode-{{ item.0 + 1 }}'
         groups: "overcloud"
         ansible_host: '{{ item.1 }}'
         inventory_ip: '{{ item.1 }}'