Add an End-to-End workflow for FUSE mount (#3562)

* Add an e2e workflow to test FUSE mount

* Fix deadlocks during concurrent r/w

weed/mount/filehandle.go

@@ -77,6 +77,10 @@ func (fh *FileHandle) AddChunks(chunks []*filer_pb.FileChunk) {
 	fh.entryLock.Lock()
 	defer fh.entryLock.Unlock()
 
+	if fh.entry == nil {
+		return
+	}
+
 	// find the earliest incoming chunk
 	newChunks := chunks
 	earliestChunk := newChunks[0]
@@ -86,10 +90,6 @@ func (fh *FileHandle) AddChunks(chunks []*filer_pb.FileChunk) {
 		}
 	}
 
-	if fh.entry == nil {
-		return
-	}
-
 	// pick out-of-order chunks from existing chunks
 	for _, chunk := range fh.entry.Chunks {
 		if lessThan(earliestChunk, chunk) {