daemon.ContainerLogs: minor debug logging cleanup

This code has many return statements, for some of them the
"end logs" or "end stream" message was not printed, giving
the impression that this "for" loop never ended.

Make sure that "begin logs" is to be followed by "end logs".

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>
(cherry picked from commit 2e4c2a6bf9cb47fd07e42f9c043024ed3dbcd04d)
Upstream-commit: 2b8bc86679b7153bb4ace063a858637df0f16a2e
Component: engine

components/engine/daemon/logs.go

@@ -118,6 +118,8 @@ func (daemon *Daemon) ContainerLogs(ctx context.Context, containerName string, c
 		defer close(messageChan)
 
 		lg.Debug("begin logs")
+		defer lg.Debugf("end logs (%v)", ctx.Err())
+
 		for {
 			select {
 			// i do not believe as the system is currently designed any error
@@ -132,14 +134,12 @@ func (daemon *Daemon) ContainerLogs(ctx context.Context, containerName string, c
 				}
 				return
 			case <-ctx.Done():
-				lg.Debugf("logs: end stream, ctx is done: %v", ctx.Err())
 				return
 			case msg, ok := <-logs.Msg:
 				// there is some kind of pool or ring buffer in the logger that
 				// produces these messages, and a possible future optimization
 				// might be to use that pool and reuse message objects
 				if !ok {
-					lg.Debug("end logs")
 					return
 				}
 				m := msg.AsLogMessage() // just a pointer conversion, does not copy data