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/volume_location_list.go

@@ -0,0 +1,65 @@
+package topology
+
+import (
+	"fmt"
+)
+
+type VolumeLocationList struct {
+	list []*DataNode
+}
+
+func NewVolumeLocationList() *VolumeLocationList {
+	return &VolumeLocationList{}
+}
+
+func (dnll *VolumeLocationList) String() string {
+	return fmt.Sprintf("%v", dnll.list)
+}
+
+func (dnll *VolumeLocationList) Head() *DataNode {
+	//mark first node as master volume
+	return dnll.list[0]
+}
+
+func (dnll *VolumeLocationList) Length() int {
+	return len(dnll.list)
+}
+
+func (dnll *VolumeLocationList) Set(loc *DataNode) {
+	for i := 0; i < len(dnll.list); i++ {
+		if loc.Ip == dnll.list[i].Ip && loc.Port == dnll.list[i].Port {
+			dnll.list[i] = loc
+			return
+		}
+	}
+	dnll.list = append(dnll.list, loc)
+}
+
+func (dnll *VolumeLocationList) Remove(loc *DataNode) bool {
+	for i, dnl := range dnll.list {
+		if loc.Ip == dnl.Ip && loc.Port == dnl.Port {
+			dnll.list = append(dnll.list[:i], dnll.list[i+1:]...)
+			return true
+		}
+	}
+	return false
+}
+
+func (dnll *VolumeLocationList) Refresh(freshThreshHold int64) {
+	var changed bool
+	for _, dnl := range dnll.list {
+		if dnl.LastSeen < freshThreshHold {
+			changed = true
+			break
+		}
+	}
+	if changed {
+		var l []*DataNode
+		for _, dnl := range dnll.list {
+			if dnl.LastSeen >= freshThreshHold {
+				l = append(l, dnl)
+			}
+		}
+		dnll.list = l
+	}
+}