Pass authentication credentials through to build

In Docker 1.10 and earlier, "docker build" can do a build FROM a private
repository that hasn't yet been pulled. This doesn't work on master. I
bisected this to https://github.com/docker/docker/pull/19414.
AuthConfigs is deserialized from the HTTP request, but not included in
the builder options.

Signed-off-by: Aaron Lehmann <aaron.lehmann@docker.com>

api/server/router/build/build_routes.go

@@ -159,6 +159,8 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *
 		buildOptions.Dockerfile = dockerfileName
 	}
 
+	buildOptions.AuthConfigs = authConfigs
+
 	out = output
 	if buildOptions.SuppressOutput {
 		out = notVerboseBuffer

integration-cli/docker_cli_build_test.go

@@ -6534,3 +6534,26 @@ func (s *DockerSuite) TestBuildWorkdirWindowsPath(c *check.C) {
 		c.Fatal(err)
 	}
 }
+
+func (s *DockerRegistryAuthSuite) TestBuildFromAuthenticatedRegistry(c *check.C) {
+	dockerCmd(c, "login", "-u", s.reg.username, "-p", s.reg.password, "-e", s.reg.email, privateRegistryURL)
+
+	baseImage := privateRegistryURL + "/baseimage"
+
+	_, err := buildImage(baseImage, `
+	FROM busybox
+	ENV env1 val1
+	`, true)
+
+	c.Assert(err, checker.IsNil)
+
+	dockerCmd(c, "push", baseImage)
+	dockerCmd(c, "rmi", baseImage)
+
+	_, err = buildImage(baseImage, fmt.Sprintf(`
+	FROM %s
+	ENV env2 val2
+	`, baseImage), true)
+
+	c.Assert(err, checker.IsNil)
+}