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/topology/allocate_volume.go

@@ -0,0 +1,35 @@
+package topology
+
+import (
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/url"
+
+	"github.com/chrislusf/seaweedfs/weed/storage"
+	"github.com/chrislusf/seaweedfs/weed/util"
+)
+
+type AllocateVolumeResult struct {
+	Error string
+}
+
+func AllocateVolume(dn *DataNode, vid storage.VolumeId, option *VolumeGrowOption) error {
+	values := make(url.Values)
+	values.Add("volume", vid.String())
+	values.Add("collection", option.Collection)
+	values.Add("replication", option.ReplicaPlacement.String())
+	values.Add("ttl", option.Ttl.String())
+	jsonBlob, err := util.Post("http://"+dn.Url()+"/admin/assign_volume", values)
+	if err != nil {
+		return err
+	}
+	var ret AllocateVolumeResult
+	if err := json.Unmarshal(jsonBlob, &ret); err != nil {
+		return fmt.Errorf("Invalid JSON result for %s: %s", "/admin/assign_volum", string(jsonBlob))
+	}
+	if ret.Error != "" {
+		return errors.New(ret.Error)
+	}
+	return nil
+}