Add support for reading logs extra attrs

The jsonlog logger currently allows specifying envs and labels that
should be propagated to the log message, however there has been no way
to read that back.

This adds a new API option to enable inserting these attrs back to the
log reader.

With timestamps, this looks like so:
```
92016-04-08T15:28:09.835913720Z foo=bar,hello=world hello
```

The extra attrs are comma separated before the log message but after
timestamps.

Without timestaps it looks like so:
```
foo=bar,hello=world hello
```

Signed-off-by: Brian Goff <cpuguy83@gmail.com>
Upstream-commit: bd9d14a07b9f1c82625dc8483245caf3fa7fe9e6
Component: engine

components/engine/integration-cli/docker_cli_logs_test.go

@@ -307,3 +307,16 @@ func (s *DockerSuite) TestLogsCLIContainerNotFound(c *check.C) {
 	message := fmt.Sprintf("Error: No such container: %s\n", name)
 	c.Assert(out, checker.Equals, message)
 }
+
+func (s *DockerSuite) TestLogsWithDetails(c *check.C) {
+	dockerCmd(c, "run", "--name=test", "--label", "foo=bar", "-e", "baz=qux", "--log-opt", "labels=foo", "--log-opt", "env=baz", "busybox", "echo", "hello")
+	out, _ := dockerCmd(c, "logs", "--details", "--timestamps", "test")
+
+	logFields := strings.Fields(strings.TrimSpace(out))
+	c.Assert(len(logFields), checker.Equals, 3, check.Commentf(out))
+
+	details := strings.Split(logFields[1], ",")
+	c.Assert(details, checker.HasLen, 2)
+	c.Assert(details[0], checker.Equals, "baz=qux")
+	c.Assert(details[1], checker.Equals, "foo=bar")
+}