volume: avoid deadlock when deleting volumes

fix https://github.com/chrislusf/seaweedfs/issues/1501

weed/storage/disk_location.go

@@ -174,9 +174,6 @@ func (l *DiskLocation) DeleteCollectionFromDiskLocation(collection string) (e er
 }
 
 func (l *DiskLocation) deleteVolumeById(vid needle.VolumeId) (found bool, e error) {
-	l.volumesLock.Lock()
-	defer l.volumesLock.Unlock()
-
 	v, ok := l.volumes[vid]
 	if !ok {
 		return

weed/storage/store.go

@@ -380,10 +380,12 @@ func (s *Store) DeleteVolume(i needle.VolumeId) error {
 		Ttl:              v.Ttl.ToUint32(),
 	}
 	for _, location := range s.Locations {
-		if found, err := location.deleteVolumeById(i); found && err == nil {
+		if err := location.DeleteVolume(i); err == nil {
 			glog.V(0).Infof("DeleteVolume %d", i)
 			s.DeletedVolumesChan <- message
 			return nil
+		} else {
+			glog.Errorf("DeleteVolume %d: %v", i, err)
 		}
 	}