topology data not dump to configuration file

[goldenrye]

Describe the bug

--cubes-dump-enable CLI option is supposed to dump the configuration for all the cubes, including the port/interface that a cube attached to, but it seems the interface was not dumped into the file

To Reproduce

Steps to reproduce the behavior:

1. Start the polycubed with option "----cubes-dump-enable --cubes-dump-file /tmp/cubes.yaml"
2. Create two Ddosmitigator cubes "dm1" and "dm2", and attach dm1 to interface "ens8"
3. Verify the configuration is in effect with polycubectl polycubectl show cubes

ddosmitigator: name uuid service-name type loglevel parent dm2 81c563d4-2d34-4c33-bd9a-5219ca738f4f ddosmitigator TC INFO dm1 71f595d7-8acb-4c25-8539-9bd97a5cdff8 ddosmitigator TC INFO ens8

4. dump the configuration file cat /tmp/cubes.yaml [ { "service-name": "ddosmitigator", "name": "dm1", "type": "TC", "loglevel": "INFO", "blacklist-src": [ { "ip": "1.1.1.1" } ] }, { "service-name": "ddosmitigator", "name": "dm2", "type": "TC", "loglevel": "INFO" ]

Expected behavior

/tmp/cubes.yaml is expected to contain the interface information and its associated cube