[improve] decommissionBookie always waiting too long time after ledgers be replicated completed

**improve**

As the Decommissioning bookie case， always change the bookie status to readonly firstly, and then wait some data expired, but always it has some ledgers (about 100+ -- 300+) legacy not be cleaned and the leaved ledgers only has little data , when we running `bin/bookkeeper shell decommissionbookie -bookieid ` to decommission the bookie , we always pending about 10 min and have not any log print, but we could find the znode /ledgers/underreplication/ledgers cleaned only few seconds and then the ledgers be rereplicate completed。

***To Reproduce***

Steps to reproduce the behavior:
1. Go to change the bookie status to readonly;
2. waiting the most ledger expired;
3. stop bookie and run `bin/bookkeeper shell decommissionbookie -bookieid `
4. See will wait long time about 10 min, even the ledgers which have few data is replicated completed, and after `Count of Ledgers which need to be rereplicated:` the log printed, the 10 min have not any other printed.

***Expected behavior***

The waiting time not too long and tell us what happened.