HDDS-1784. Missing HostName and IpAddress in the response of register command.

(cherry picked from commit 0f399b0d57875c64f49df3942743111905fd2198)

hadoop-hdds/server-scm/src/main/java/org/apache/hadoop/hdds/scm/server/SCMDatanodeProtocolServer.java

@@ -271,6 +271,8 @@ public class SCMDatanodeProtocolServer implements
         .setErrorCode(cmd.getError())
         .setClusterID(cmd.getClusterID())
         .setDatanodeUUID(cmd.getDatanodeUUID())
+        .setIpAddress(cmd.getIpAddress())
+        .setHostname(cmd.getHostName())
         .build();
   }