Fixing typo and potential memory problem.
Reducing number of concurrent mysqlslap threads since tests fail
in pushbuild due to too many threads.


mysql-test/r/rpl_insert.result:
  Result change.
mysql-test/t/rpl_insert.test:
  Reducing number of threads since it doesn't pass pushbuild.
sql/sql_insert.cc:
  Fixing typo and potential memory problem.