Fix a race on some platforms in mysql-test-run.pl, where it would sometimes errorneously abort reporting failure to kill child processes, where in reality the problem was merely that the child had become a zombie because of missing waitpid() call.
Fix a race on some platforms in mysql-test-run.pl, where it would sometimes
errorneously abort reporting failure to kill child processes, where in
reality the problem was merely that the child had become a zombie because
of missing waitpid() call.


mysql-test/lib/mtr_process.pl:
  Fix race (on some platforms) when killing processes.

flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,natsys/mariadb_10.2,flynn1973/mariadb-aix,davidl-zend/zenddbi,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,slanterns/server,flynn1973/mariadb-aix,flynn1973/mariadb-aix,davidl-zend/zenddbi,flynn1973/mariadb-aix,flynn1973/mariadb-aix,ollie314/server,natsys/mariadb_10.2,ollie314/server,flynn1973/mariadb-aix,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,natsys/mariadb_10.2,ollie314/server,ollie314/server,natsys/mariadb_10.2,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,flynn1973/mariadb-aix,davidl-zend/zenddbi,davidl-zend/zenddbi,flynn1973/mariadb-aix,natsys/mariadb_10.2,ollie314/server,davidl-zend/zenddbi,davidl-zend/zenddbi,davidl-zend/zenddbi,ollie314/server