Refactor multiplex and simple channel managers to avoid copy pasted code.

RB_ID=138789
 Improve logging in hedwig-server
 - Improve logging in package topics
 - Improve logging in package subscriptions
 - Improve logging for package persistence
 - Improve logging in package handlers
 - Improve logging for package delivery
 - Improve logging in package netty

RB_ID=138892
improve logging for bookkeeper (3rd part : meta & zookeeper package)
- - add log statement to track zookeeper client state so we know what happened for zookeeper client.
- improve log statements in bookkeeper meta package.

RB_ID=138728
improve logging in bookkeeper (second part : client & proto package)
- dump version with ledger metadata, so it would be easy to check what happened when metadata version conflicts.
- added missing exception stack and return value.
- added final if necessary and cleanup imports when touching that file

RB_ID=138715
improve logging in bookkeeper (first part : bookie package)
- improve logging statements in bookie package
- making immutable variables to final and cleanup imports when touching that file
- removed unused MarkerFileChannel (since it is never used)

RB_ID=138531
toString for LastLogMark

RB_ID=139102
 Don't close the channel from the subscribe handler in case of error
 - Don't close the channel from the subscribe handler in case of error
 Multiplexed subscription channels can have failures for a subset of topics and other topics should not suffer because of this.

RB_ID=139266
Hedwig Client Logging - Part 1
Logging in Handlers

RB_ID=138788