OnStop_timeout test occasionally fails

[sywhang]

TestAppRunTimeout/OnStop timeout test occasionally fails on Windows leg because the Stopped event isn't emitted for some reason. Probably a flaky test and we should fix this.

FIND: Parameter format not correct
go test -race -coverprofile=cover.out -coverpkg=./... ./...
--- FAIL: TestAppRunTimeout (0.00s)
    --- FAIL: TestAppRunTimeout/OnStop_timeout (0.00s)
        app_test.go:828: 
            	Error Trace:	app_test.go:828
            	Error:      	"[]" should have 1 item(s), but has 0
            	Test:       	TestAppRunTimeout/OnStop_timeout
            	Messages:   	expected a "Stopped" event
FAIL

Ref: GO-1001

[sywhang]

Update: looks like it happens everywhere, not just Windows. It repros very rarely on my local dev machine (1/200 runs) but in CI it happens more frequently.