Fix Ansible inventory generation when reusing group names

When a kolla-ansible group is composed of a kayobe group with the same
name and of at least one other kayobe group, kayobe would generate an
invalid Ansible inventory such as:

[compute:children]
controllers
compute

Because the top-level group should already be defined, we only need to
add as children the kayobe groups using different names.

Change-Id: I88bdf1e3d0c08271ac8938ae2f9ac3f9fee1efa5
Story: 2009927
Task: 44798