Erasure Coding: allocate and persist striped blocks in NameNode

Try to finish the remaining work from HDFS-7339 (except the ClientProtocol/DFSClient part):

1. Allow FSNamesystem#getAdditionalBlock to create striped blocks and persist striped blocks to editlog
2. Update FSImage for max allocated striped block ID
3. Update the block commit/complete logic in BlockManager