libuv API misuse

[MathieuBordere]

Aug 02 08:17:25 soetomodb2 microk8s.daemon-apiserver[15684]: kube-apiserver: src/unix/poll.c:109: uv_poll_stop: Assertion `!uv__is_closing(handle)' failed.
Aug 02 08:17:26 soetomodb2 systemd[1]: snap.microk8s.daemon-apiserver.service: Main process exited, code=killed, status=6/ABRT

Possibly

raft/src/uv_writer.c

Line 379 in b71e303

rv = uv_poll_stop(&w->event_poller);

is hit when the fd is already closed, triggering the assertion in https://github.com/libuv/libuv/blob/04289fa326b790c1a4abb236d1f9d913bacfc8c6/src/unix/poll.c#L113

Also see canonical/microk8s#2487

[pedroleaoc]

Closing this one for now.