[APIv2] /networks/prune endpoint has wrong response format

[riyad]

Is this a BUG REPORT or FEATURE REQUEST? (leave only one on its own line)

/kind bug

Description

Trying to find regressions by exercising the APIv2 trough docker-py's test suite (see #5386) I came across the failing TestNetworks::test_prune_networks test.

It seems that the Podman 3.0.0-dev /networks/prune endpoint wrongly returns the list of deleted networks directly [...] (instead of nesting them according to the Docker API docs).

Steps to reproduce the issue:

$ curl -sS --unix-socket /var/run/user/1000/podman/podman.sock -XPOST 'http://localhost/v1.40/networks/create' -H "Content-Type: application/json" -d '{"Name": "dockerpytest_6a208c32613d1dde"}'
{"Id":"f5e714d4689079d34aa0b0f1d8a11f930da56bb66e1a450f31727776b9029a1c","Warning":null}

$ curl -sS --unix-socket /var/run/user/1000/podman/podman.sock -XPOST 'http://localhost/v1.40/networks/prune'                                                                                   
["dockerpytest_6a208c32613d1dde"]

Describe the results you received:

The response looked like 200 ["<network name>", ...]

Describe the results you expected:

The response should look like 200 {"NetworksDeleted": ["<network name>", ...]}

Additional information you deem important (e.g. issue happens only occasionally):

Docker API docs: https://docs.docker.com/engine/api/v1.40/#operation/NetworkPrune

[baude]

thanks for the excellent write up!