docker: minikube delete should delete the network

[medyagh]

I notice minikube delete doesn't remoev the network after itself. created this issue.

medya@medya:~/workspace/minikube (master)$ ./out/minikube delete --all

medya@medya:~/workspace/minikube (master)$ docker network ls
NETWORK ID          NAME                DRIVER              SCOPE
fdc833b38ce5        bridge              bridge              local
43cf4c7ad471        host                host                local
0e6c505503f2        minikube            bridge              local
2d7623149fc1        none                null                local