Add system time to /info

This change adds daemon's system time as RFC3339Nano to the `/info` endpoint
and shows in a more readable format (UnixDate) in `docker -D info` output.

I will be using this to fix the clock skew between the remote test host and
the CI machines running `docker events`-related tests as they're using `--since`
and `--until` and the timestamps are not matching when daemon is not on the
same machine.

Signed-off-by: Ahmet Alp Balkan <ahmetalpbalkan@gmail.com>

daemon/info.go

@@ -3,6 +3,7 @@ package daemon
 import (
 	"os"
 	"runtime"
+	"time"
 
 	log "github.com/Sirupsen/logrus"
 	"github.com/docker/docker/autogen/dockerversion"
@@ -76,6 +77,7 @@ func (daemon *Daemon) CmdInfo(job *engine.Job) engine.Status {
 	v.SetBool("Debug", os.Getenv("DEBUG") != "")
 	v.SetInt("NFd", utils.GetTotalUsedFds())
 	v.SetInt("NGoroutines", runtime.NumGoroutine())
+	v.Set("SystemTime", time.Now().Format(time.RFC3339Nano))
 	v.Set("ExecutionDriver", daemon.ExecutionDriver().Name())
 	v.SetInt("NEventsListener", env.GetInt("count"))
 	v.Set("KernelVersion", kernelVersion)