fusefs: reenable the WriteCluster.cluster_write_err test
The underlying panic was just fixed by
revision 27006229f7a40a18a61a0e8fd270bc583326b690
PR: 238565
MFC with: 27006229f7a40a18a61a0e8fd270bc583326b690
(cherry picked from commit 425bbe9e64f7af6bdb30a099bd90a32885de1ab8)