In the ha_partition::position() we don't calculate the number
of the partition of the record, but use m_last_part value instead,
relying on that it's previously set by some other call like ::write_row().
Delete_rows_log_event::do_exec_row() calls find_and_fetch_row(),
where we used position() + rnd_pos() call for the InnoDB-based PARTITION-ed
table as there HA_PRIMARY_KEY_REQUIRED_FOR_POSITION enabled.

fixed by introducing new handler::rnd_pos_by_record() method to be
used for random record-based positioning


sql/ha_partition.cc:
  Bug #28430 Failure in replication of innodb partitioned tables on row/mixed format.
  
  ha_partition::rnd_pos_by_record() implemented
sql/ha_partition.h:
  Bug #28430 Failure in replication of innodb partitioned tables on row/mixed format.
  
  ha_partition::rnd_pos_by_record() declared
sql/handler.h:
  Bug #28430 Failure in replication of innodb partitioned tables on row/mixed format.
  
  handler::rnd_pos_by_record() introduced
sql/log_event.cc:
  Bug #28430 Failure in replication of innodb partitioned tables on row/mixed format.
  
  handler::rnd_pos_by_record used instead of position() + rnd_pos() call