TableInputFormatBase getSplitKey does not handle signed bytes correctly

When auto-balance is enabled in TableInputFormatBase and the table key is a binary key, the getSplitKey method does not function correctly for signed bytes. The proposed solution it to utilize org.apache.hadoop.hbase.util.Bytes#split method to find the split key. org.apache.hadoop.hbase.util.Bytes#split is stated to be a expensive operation, so if another solution is preferred, that is fine. In addition, handling of a split key that is equal to the TableSplit end key is added to calculateRebalancedSplits.