use pubsub instead of filenotify to follow json logs

inotify event is trigged immediately there's data written to disk.
But at the time that the inotify event is received, the json line might
not fully saved to disk. If the json decoder tries to decode in such
case, an io.UnexpectedEOF will be trigged.
We used to retry for several times to mitigate the io.UnexpectedEOF error.
But there are still flaky tests caused by the partial log entries.

The daemon knows exactly when there are new log entries emitted. We can
use the pubsub package to notify all the log readers instead of inotify.

Signed-off-by: Shijiang Wei <mountkin@gmail.com>

try to fix broken test. will squash once tests pass

Signed-off-by: Shijiang Wei <mountkin@gmail.com>
Upstream-commit: b1594c59f5e0d1ac898eacde8d91b1ba33c2b626
Component: engine

components/engine/pkg/pubsub/publisher.go

@@ -54,8 +54,10 @@ func (p *Publisher) SubscribeTopic(topic topicFunc) chan interface{} {
 // Evict removes the specified subscriber from receiving any more messages.
 func (p *Publisher) Evict(sub chan interface{}) {
 	p.m.Lock()
-	delete(p.subscribers, sub)
-	close(sub)
+	if _, ok := p.subscribers[sub]; ok {
+		delete(p.subscribers, sub)
+		close(sub)
+	}
 	p.m.Unlock()
 }