fusefs: fix intermittency in some ENOENT tests

When a FUSE operation other than LOOKUP returns ENOENT, the kernel will
reclaim that vnode, resuling in a FUSE_FORGET being sent a short while
later. Many of the ENOENT tests weren't expecting those FUSE_FORGET
operations. They usually passed by luck since FUSE_FORGET is often delayed.
This commit adds appropriate expectations.

MFC after: 2 weeks