Make daemon to start with no userlandproxy by default

This PR makes a user visible behavior change with userland
proxy disabled by default and rely on hairpin NAT to be enabled
by default. This may not work in older (unsupported) kernels
where the user will be forced to enable userlandproxy if needed.

      - Updated the Docs
      - Changed the integration-cli to start with userlandproxy
	desiabled by default.

Signed-off-by: Jana Radhakrishnan <mrjana@docker.com>

integration-cli/docker_cli_daemon_test.go

@@ -860,7 +860,6 @@ func (s *DockerDaemonSuite) TestDaemonIP(c *check.C) {
 	out, err := d.Cmd("run", "-d", "-p", "8000:8000", "busybox", "top")
 	c.Assert(err, check.NotNil,
 		check.Commentf("Running a container must fail with an invalid --ip option"))
-	c.Assert(strings.Contains(out, "Error starting userland proxy"), check.Equals, true)
 
 	ifName := "dummy"
 	out, err = createInterface(c, "dummy", ifName, ipStr)

integration-cli/docker_utils.go

@@ -69,7 +69,7 @@ func NewDaemon(c *check.C) *Daemon {
 		c.Fatalf("Could not create %s/graph directory", daemonFolder)
 	}
 
-	userlandProxy := true
+	userlandProxy := false
 	if env := os.Getenv("DOCKER_USERLANDPROXY"); env != "" {
 		if val, err := strconv.ParseBool(env); err != nil {
 			userlandProxy = val