there is a mistake about 'MaterializeTupleTime' for kudu

hi,
i find that the 'MaterializeTupleTime' for kuduScanner is very different from hdfsScanner while reading impala's profile.
in 'class HdfsParquetScanner' there is a timer named 'ScopedTimer<MonotonicStopWatch> assemble_rows_timer_', but in 'class KuduScanner' there is not.
maybe we need to add the timer for kuduScanner, just like hdfsScanner does.