Let MYSQL_CLIENT_TEST be set with command line from mysql-test-run script
mysql-test-run.sh:
  Renamed client_test to mysql_client_test
  Support --embedded-server test on installed server
mysql_client_test.test:
  Renamed client_test to mysql_client_test
  Use env var CLIENT_TEST with full name, it differs when run with --embedded-server
  Rename: mysql-test/t/client_test.test -> mysql-test/t/mysql_client_test.test