add 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>

integration-cli/docker_cli_prune_unix_test.go

@@ -0,0 +1,61 @@
+// +build !windows
+
+package main
+
+import (
+	"strconv"
+	"strings"
+
+	"github.com/docker/docker/pkg/integration/checker"
+	"github.com/go-check/check"
+)
+
+func pruneNetworkAndVerify(c *check.C, d *SwarmDaemon, kept, pruned []string) {
+	_, err := d.Cmd("network", "prune", "--force")
+	c.Assert(err, checker.IsNil)
+	out, err := d.Cmd("network", "ls", "--format", "{{.Name}}")
+	c.Assert(err, checker.IsNil)
+	for _, s := range kept {
+		c.Assert(out, checker.Contains, s)
+	}
+	for _, s := range pruned {
+		c.Assert(out, checker.Not(checker.Contains), s)
+	}
+}
+
+func (s *DockerSwarmSuite) TestPruneNetwork(c *check.C) {
+	d := s.AddDaemon(c, true, true)
+	_, err := d.Cmd("network", "create", "n1") // used by container (testprune)
+	c.Assert(err, checker.IsNil)
+	_, err = d.Cmd("network", "create", "n2")
+	c.Assert(err, checker.IsNil)
+	_, err = d.Cmd("network", "create", "n3", "--driver", "overlay") // used by service (testprunesvc)
+	c.Assert(err, checker.IsNil)
+	_, err = d.Cmd("network", "create", "n4", "--driver", "overlay")
+	c.Assert(err, checker.IsNil)
+
+	cName := "testprune"
+	_, err = d.Cmd("run", "-d", "--name", cName, "--net", "n1", "busybox", "top")
+	c.Assert(err, checker.IsNil)
+
+	serviceName := "testprunesvc"
+	replicas := 1
+	out, err := d.Cmd("service", "create", "--name", serviceName,
+		"--replicas", strconv.Itoa(replicas),
+		"--network", "n3",
+		"busybox", "top")
+	c.Assert(err, checker.IsNil)
+	c.Assert(strings.TrimSpace(out), checker.Not(checker.Equals), "")
+	waitAndAssert(c, defaultReconciliationTimeout, d.checkActiveContainerCount, checker.Equals, replicas+1)
+
+	// prune and verify
+	pruneNetworkAndVerify(c, d, []string{"n1", "n3"}, []string{"n2", "n4"})
+
+	// remove containers, then prune and verify again
+	_, err = d.Cmd("rm", "-f", cName)
+	c.Assert(err, checker.IsNil)
+	_, err = d.Cmd("service", "rm", serviceName)
+	c.Assert(err, checker.IsNil)
+	waitAndAssert(c, defaultReconciliationTimeout, d.checkActiveContainerCount, checker.Equals, 0)
+	pruneNetworkAndVerify(c, d, []string{}, []string{"n1", "n3"})
+}