[Bug] Always one orphan ledger is created

**BUG REPORT**

***Describe the bug***

Each time after a ledger is created, there will be one more orphan ledger with size 0 created as well, which can't be tracked.

***To Reproduce***

Steps to reproduce the behavior:
1. list ledgers before creation
2. DistributedLogManager#openLogWriter
3. LogWriter#write(LogRecord)
4. LogWriter#close
5. list ledgers. Compared with 1. you will find 2 more ledgers

***Expected behavior***

Should be only 1 ledger

***Screenshots***

N/A

***Root Cause***

The root cause lies in the **BKLogWriteHandler#doStartLogSegment**
line 571: it calls **logSegmentAllocator.allocate();**, which is, in fact, SimpleLedgerAllocator#allocate.
Then inside SimpleLedgerAllocator#allocate, whenComplete -> onSuccess, it will mark phase: **ALLOCATED**.
But just one line after, inside **completeAllocation**, it adds one ZKSetVersionTxn (together with SimpleLedgerAllocator as listner) and marks the phase back to **HANDING_OVER**

So here now we back to **BKLogWriteHandler#doStartLogSegment**,
line 579, started a ZK Transactiion
line 661, txn.execute -> ZKTransaction#processResult -> ZKSetVersionTxn#commitOpResult -> listener#onCommit() (listener is SimpleLedgerAllocator, so it is SimpleLedgerAllocator#onCommit) --> SimpleLedgerAllocator#confirmObtain.

Inside the SimpleLedgerAllocator#confirmObtain, as the phase is changed back to **HANDING_OVER**, there **shouldAllocate = true;**, and this is the where the orphan ledger comes from