public static KeyValue previousKey(final KeyValue in) {
    return createFirstOnRow(CellUtil.cloneRow(in), CellUtil.cloneFamily(in),
      CellUtil.cloneQualifier(in), in.getTimestamp() - 1);
  }
Decrement the timestamp. For tests (currently wasteful) Remember timestamps are sorted reverse
chronologically.
@return previous key
hbase-common/src/main/java/org/apache/hadoop/hbase/KeyValueUtil.java