Check for both config.yaml/config.json
Check for both config.yaml/config.json

We changed the format of network config generated from json
to yaml when we moved to use ansible for network configuration.
This resulted in _validate_no_ip_change() preflight validation
being useless when net_config_override is not used.

Change-Id: I1a2a6b817b32bc5c95cd4810dc3cca43366d717a

openstack/python-tripleoclient