clusterCreate/network: only use the exact chosen network

Before, we just looked up the name of the docker network, causing docker
to do some sort of relaxed matching (prefix?) which could cause k3d to
choose the first matching network instead of the exact match.
Now we're enforcing exact Regex matching to prevent this.
Fixes #374

pkg/runtimes/docker/network.go

@@ -23,6 +23,7 @@ package docker
 
 import (
 	"context"
+	"fmt"
 	"net"
 
 	"github.com/docker/docker/api/types"
@@ -46,12 +47,12 @@ func (d Docker) CreateNetworkIfNotPresent(ctx context.Context, name string) (str
 	defer docker.Close()
 
 	// (1) configure list filters
-	args := filters.NewArgs()
-	args.Add("name", name)
+	filter := filters.NewArgs()
+	filter.Add("name", fmt.Sprintf("^/?%s$", name)) // regex filtering for exact name match
 
 	// (2) get filtered list of networks
 	networkList, err := docker.NetworkList(ctx, types.NetworkListOptions{
-		Filters: args,
+		Filters: filter,
 	})
 	if err != nil {
 		log.Errorln("Failed to list docker networks")