Many dump threads can exist due to a way the new version of mtr governs suites.

For this immediate problem the test is refined not to use I_S but rather to reconnect
explicitly with preserving logics of a an old target bug fixes verification.

mysql-test/suite/rpl/r/rpl_temporary.result:
  results changed
mysql-test/suite/rpl/t/rpl_temporary.test:
  refining the bug#17284 test to avoid counting dump threads in favor to reconnect
  explicitly with preserving the orig logics.