Problem: the test failed because errors were found in the error log.
The test case contains suppressions for an old version of the error message,
but the format of the error message has changed without updating the suppression.
Fix: Update the suppression. Also small fixes to improve the test.


mysql-test/suite/rpl/r/rpl_slave_load_remove_tmpfile.result:
  update result file
mysql-test/suite/rpl/t/rpl_slave_load_remove_tmpfile-slave.opt:
  Use variables instead of .opt files to avoid server restarts.
mysql-test/suite/rpl/t/rpl_slave_load_remove_tmpfile.test:
  1. To fix the bug, we update the regular expression in mtr.add_suppression
     so that it matches the real error text.
  2. Use wait_for_slave_sql_error.inc when we wait for an error.
     This makes the test easier to understand and will produce better
     debug info if the test fails.
  3. Use server variables instead of command line options to set
     the @@GLOBAL.DEBUG variable. This avoids server restarts when
     running the test suite.
  4. Clarify the comment at the top of the file and add bug reference.