Figure out the source of the occasional fsnotify test failures

Every once in a while, there are test failures in the `aghnet` package, most of which are linked in one way or another to the `github.com/fsnotify/fsnotify` module. These failures are annoying, and we should investigate, why they happen and how can we prevent them. Perhaps there is a kind of filesystem race condition there?

An example of such failure:

```none
=== RUN TestEtcHostsContainerFSNotify
=== RUN TestEtcHostsContainerFSNotify/unknown_host
=== RUN TestEtcHostsContainerFSNotify/notified
etchostscontainer_test.go:126:
Error Trace: etchostscontainer_test.go:126
Error: Expected value not to be nil.
Test: TestEtcHostsContainerFSNotify/notified
etchostscontainer_test.go:127:
Error Trace: etchostscontainer_test.go:127
Error: "[]" should have 1 item(s), but has 0
Test: TestEtcHostsContainerFSNotify/notified
--- FAIL: TestEtcHostsContainerFSNotify (0.19s)
--- PASS: TestEtcHostsContainerFSNotify/unknown_host (0.00s)
--- FAIL: TestEtcHostsContainerFSNotify/notified (0.00s)
```