fuse: stop spamming stderr for failing fusermount.

fuse/mountstate.go

@@ -168,13 +168,15 @@ func (ms *MountState) Unmount() (err error) {
 			break
 		}
 
-		fmt.Fprintf(os.Stderr, "umount failed; retrying\n")
 		// Sleep for a bit. This is not pretty, but there is
 		// no way we can be certain that the kernel thinks all
 		// open files have already been closed.
 		delay = 2*delay + 5*time.Millisecond
 		time.Sleep(delay)
 	}
+	if err != nil {
+		return 
+	}
 	// Wait for event loops to exit.
 	ms.loops.Wait()
 	ms.mountPoint = ""