Attempting to create a GCE cluster when the `gce.ini` configuration file
contains a non-default network leads to the following error:
```
TASK [Launch instance(s)] ******************************************************
fatal: [localhost]: FAILED! => {"changed": false, "failed": true, "msg": "Unexpected error attempting to create instance lenaic2-master-74f10, error: {'domain': 'global', 'message': \"Invalid value for field 'resource.networkInterfaces[0]': ''. Subnetwork should be specified for custom subnetmode network\", 'reason': 'invalid'}"}
```

The `subnetwork` parameter needs to be added and taken into account.