filer: leveldb, rocksdb auto create store directory

fix https://github.com/chrislusf/seaweedfs/issues/1901

weed/filer/rocksdb/rocksdb_store.go

@@ -8,6 +8,7 @@ import (
 	"crypto/md5"
 	"fmt"
 	"io"
+	"os"
 
 	"github.com/tecbot/gorocksdb"
 
@@ -56,6 +57,7 @@ func (store *RocksDBStore) Initialize(configuration weed_util.Configuration, pre
 
 func (store *RocksDBStore) initialize(dir string) (err error) {
 	glog.Infof("filer store rocksdb dir: %s", dir)
+	os.MkdirAll(dir, 0755)
 	if err := weed_util.TestFolderWritable(dir); err != nil {
 		return fmt.Errorf("Check Level Folder %s Writable: %s", dir, err)
 	}