directory structure change to work with glide

glide has its own requirements. My previous workaround caused me some
code checkin errors. Need to fix this.

weed/command/volume_test.go

@@ -0,0 +1,13 @@
+package command
+
+import (
+	"net/http"
+	"testing"
+	"time"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+func TestXYZ(t *testing.T) {
+	glog.V(0).Infoln("Last-Modified", time.Unix(int64(1373273596), 0).UTC().Format(http.TimeFormat))
+}