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>

engine/env_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/json"
 	"testing"
+	"time"
 
 	"github.com/docker/docker/pkg/testutils"
 )
@@ -94,6 +95,27 @@ func TestSetenvBool(t *testing.T) {
 	}
 }
 
+func TestSetenvTime(t *testing.T) {
+	job := mkJob(t, "dummy")
+
+	now := time.Now()
+	job.SetenvTime("foo", now)
+	if val, err := job.GetenvTime("foo"); err != nil {
+		t.Fatalf("GetenvTime failed to parse: %v", err)
+	} else {
+		nowStr := now.Format(time.RFC3339)
+		valStr := val.Format(time.RFC3339)
+		if nowStr != valStr {
+			t.Fatalf("GetenvTime returns incorrect value: %s, Expected: %s", valStr, nowStr)
+		}
+	}
+
+	job.Setenv("bar", "Obviously I'm not a date")
+	if val, err := job.GetenvTime("bar"); err == nil {
+		t.Fatalf("GetenvTime was supposed to fail, instead returned: %s", val)
+	}
+}
+
 func TestSetenvInt(t *testing.T) {
 	job := mkJob(t, "dummy")