Use DBStore instead of MetadataStore in SCM

The MetadataStore interface provides a generic view to any key / value store with a LevelDB and RocksDB implementation.

Since the early version of MetadataStore we also go the DBStore interface which is more andvanced (it supports DB profiles and ColumnFamilies).

To simplify the introduction of new features (like versioning or rocksdb tuning) we should use the new interface everywhere instead of the old interface.

We should update SCM and Datanode to use the DBStore instead of MetadataStore.