Improve 'run_testcase_need_slave_restart' to detect if a slave restart really is necessary. 
So far all rpl test requires a slave restart, but for all other tests it can be skipped
Improve the sort order used by --reorder


mysql-test/lib/mtr_cases.pl:
  Improve the sort order used by reorder
mysql-test/mysql-test-run.pl:
  Improve 'run_testcase_need_master_restart' to require restart if master is not already started
  Improve 'run_testcase_need_slave_restart' to detect if a slave restart really is necessary. 
  So far all rpl test requires a slave restart, but for all other tests it can be skipped