Accidently removed public API of FileTxnLog.setPreallocSize()

In my latest commit regarding TxnLogToolkit there's a refactor to outsource file padding logic from FileTxnLog to a separate class:

https://github.com/apache/zookeeper/commit/126fb0f22d701cad58bf3123bf7d8f2219e60387#diff-89717124564925d61d29dd817bcdd915

Unfortunately public static method setPreallocSize(int) has also been moved to the new class, but it's being actively used by hadoop-common project too:

https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/ha/ClientBaseWithFixes.java#L384

I'd like to submit a patch to revert the deleted method which is going to call the new one, but will keep backward compatibility with Hadoop.