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/stats/disk.go

@@ -0,0 +1,14 @@
+package stats
+
+type DiskStatus struct {
+	Dir  string
+	All  uint64
+	Used uint64
+	Free uint64
+}
+
+func NewDiskStatus(path string) (disk *DiskStatus) {
+	disk = &DiskStatus{Dir: path}
+	disk.fillInStatus()
+	return
+}