Javadoc
Open-Fences this BookKeeper log using the following protocol:
1. Read Log Metadata from ZooKeeper.
2. Fence at least the last 2 ledgers in the Ledger List.
3. Create a new Ledger.
3.1 If any of the steps so far fails, the process is interrupted at the point of failure, and no cleanup is attempted.
4. Update Log Metadata using compare-and-set (this update contains the new ledger and new epoch).
4.1 If CAS fails on metadata update, the newly created Ledger is deleted (this means we were fenced out by some
other instance) and no other update is performed.