reference_group [1] is a key used to filter out provider_networks
assignment to containers more easily. So one can use same group_binds
but execute extra filtering using reference_group. This is especially
useful in multi-pod or multi-az deployments.
However, currently reference_group expects always to find hosts directly
in the group, but not looking inside children groups.
The patch changes the logic of how reference_group lookups for the
hosts in group by descending into each child and populating the list to
compare with.
[1] https://docs.openstack.org/openstack-ansible/latest/user/l3pods/example.html#environment-layout
Change-Id: I7faccad43e55692656ba3046165e6eecd38a9984
120c942fda