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/storage/disk_location.go

@@ -0,0 +1,73 @@
+package storage
+
+import (
+	"io/ioutil"
+	"strings"
+
+	"github.com/chrislusf/seaweedfs/weed/glog"
+)
+
+type DiskLocation struct {
+	Directory      string
+	MaxVolumeCount int
+	volumes        map[VolumeId]*Volume
+}
+
+func NewDiskLocation(dir string, maxVolumeCount int) *DiskLocation {
+	location := &DiskLocation{Directory: dir, MaxVolumeCount: maxVolumeCount}
+	location.volumes = make(map[VolumeId]*Volume)
+	return location
+}
+
+func (l *DiskLocation) loadExistingVolumes(needleMapKind NeedleMapType) {
+
+	if dirs, err := ioutil.ReadDir(l.Directory); err == nil {
+		for _, dir := range dirs {
+			name := dir.Name()
+			if !dir.IsDir() && strings.HasSuffix(name, ".dat") {
+				collection := ""
+				base := name[:len(name)-len(".dat")]
+				i := strings.LastIndex(base, "_")
+				if i > 0 {
+					collection, base = base[0:i], base[i+1:]
+				}
+				if vid, err := NewVolumeId(base); err == nil {
+					if l.volumes[vid] == nil {
+						if v, e := NewVolume(l.Directory, collection, vid, needleMapKind, nil, nil); e == nil {
+							l.volumes[vid] = v
+							glog.V(0).Infof("data file %s, replicaPlacement=%s v=%d size=%d ttl=%s", l.Directory+"/"+name, v.ReplicaPlacement, v.Version(), v.Size(), v.Ttl.String())
+						} else {
+							glog.V(0).Infof("new volume %s error %s", name, e)
+						}
+					}
+				}
+			}
+		}
+	}
+	glog.V(0).Infoln("Store started on dir:", l.Directory, "with", len(l.volumes), "volumes", "max", l.MaxVolumeCount)
+}
+
+func (l *DiskLocation) DeleteCollectionFromDiskLocation(collection string) (e error) {
+	for k, v := range l.volumes {
+		if v.Collection == collection {
+			e = l.deleteVolumeById(k)
+			if e != nil {
+				return
+			}
+		}
+	}
+	return
+}
+
+func (l *DiskLocation) deleteVolumeById(vid VolumeId) (e error) {
+	v, ok := l.volumes[vid]
+	if !ok {
+		return
+	}
+	e = v.Destroy()
+	if e != nil {
+		return
+	}
+	delete(l.volumes, vid)
+	return
+}