Given the other Jiras under
HDFS-13541, this Jira is to allow DFSClient to redirect the encrypt secret to DataNode. The encrypted message is the QOP that client and NameNode have used. DataNode decrypts the message and enforce the QOP for the client connection. Also, this Jira will also include overwriting downstream QOP, as mentioned in the HDFS-13541 design doc. Namely, this is to allow inter-DN QOP that is different from client-DN QOP.