WL#3397 Refactoring storage engine test cases (for falcon)
      It contains fixes according to second code review.
- Remove any occurence of hardcoded assignments of storage engines
- Use variable names exact telling what it is used for
- Updated comments
- remove trailing spaces


mysql-test/include/handler.inc:
  - Replace hardcoded MyISAM with assignments via variable
mysql-test/include/mix1.inc:
  - Replace hardcoded MyISAM with assignments via variable
  - Remove hardcoded InnoDB assignments (They were introduced by late push)
  - Remove trailing spaces
mysql-test/include/mix2.inc:
  - Replace hardcode MyISAM assignments
  - Remove trailing spaces
  - Engine assignments via variable refers to the use of the storage engine
    $other_non_trans_engine_type, $other_live_chcks_engine_type ...
mysql-test/include/read_many_rows.inc:
  Replace hardcoded MyISAM assignment
mysql-test/include/rowid_order.inc:
  remove trailing spaces
mysql-test/r/handler_innodb.result:
  Updated result
mysql-test/r/handler_myisam.result:
  Updated result
mysql-test/r/innodb_mysql.result:
  Updated result
mysql-test/r/mix2_myisam.result:
  Updated result
mysql-test/r/read_many_rows_innodb.result:
  Updated result
mysql-test/r/rowid_order_innodb.result:
  Updated result
mysql-test/t/handler_innodb.test:
  Introduce $variables
mysql-test/t/handler_myisam.test:
  Introduce $variables
mysql-test/t/mix2_myisam.test:
  Introduce $variables
mysql-test/t/read_many_rows_innodb.test:
  Introduce $variables