MariaRocks: make rocksdb.rocksdb_datadir test pass

The test runs $MYSQLD_BOOTSTRAP_CMD but that command does not include
arguments for loading ha_rocksdb.so plugin. Add them.

storage/rocksdb/mysql-test/rocksdb/t/rocksdb_datadir.test

@@ -19,8 +19,9 @@ EOF
 # Must ensure this directory exists before launching mysqld
 mkdir $ddir;
 
+let $plugin_dir=`select @@plugin_dir`;
 # Launch mysqld with non-standard rocksdb_datadir
-exec $MYSQLD_BOOTSTRAP_CMD --datadir=$ddir --rocksdb_datadir=$rdb_ddir --default-storage-engine=rocksdb --skip-innodb --default-tmp-storage-engine=MyISAM --rocksdb < $sql_file;
+exec $MYSQLD_BOOTSTRAP_CMD --plugin-dir=$plugin_dir --plugin-load=$HA_ROCKSDB_SO --datadir=$ddir --rocksdb_datadir=$rdb_ddir --default-storage-engine=rocksdb --skip-innodb --default-tmp-storage-engine=MyISAM --rocksdb < $sql_file;
 
 --echo Check for the number of MANIFEST files
 exec ls $rdb_ddir/MANIFEST-0000* | wc -l;