Inaccurate arithmetic operation in LookupTableToHFileJob#calculateShardNum

There're two issues with the following code:

    private int calculateShardNum(KylinConfig kylinConfig, long dataSize) {
        long shardSize = kylinConfig.getExtTableSnapshotShardingMB() * 1024 * 1024;
        return dataSize < shardSize ? 1 : (int) (Math.ceil(dataSize / shardSize));

getExtTableSnapshotShardingMB returns an int. The multiplication is done using 32-bit arithmetic, and then used in a context that expects an expression of type "long".

Second, Math.ceil expects a double. The integer division would lose some precision.