MariaRocks port: put MyRocks options into rocksdb/my.cnf

- Before this, one had to provide appropriate --mysqld=.... options to
  mysql-test-run.

- Also moved one option from rocksdb/suite.opt to rocksdb/my.cnf.

storage/rocksdb/mysql-test/rocksdb/my.cnf

 !include include/default_my.cnf
 
 [server]
+rocksdb
+skip-innodb
+default-storage-engine=rocksdb
+
+ignore-db-dirs=.rocksdb
+
 sql-mode=NO_ENGINE_SUBSTITUTION
 explicit-defaults-for-timestamp=1
 rocksdb_lock_wait_timeout=1

storage/rocksdb/mysql-test/rocksdb/suite.opt

---ignore-db-dirs=.rocksdb