docker network prune
`docker network prune` prunes unused networks, including overlay ones. `docker system prune` also prunes unused networks. Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp> Upstream-commit: 7e24c16086a9a4f38e241e51837f2be4877c04a6 Component: engine
Signed-off-by: allencloud <allen.sun@daocloud.io> Upstream-commit: fd62b6c9505451670b926216648ab7f6a3f9f586 Component: engine
Signed-off-by: Kenfe-Mickael Laventure <mickael.laventure@gmail.com> Upstream-commit: 280c8723667af385e0807a090ddc5cc57c46807e Component: engine