3.2.x upgrade to 3.3

[Jason Wen]

Hi All,

I see a significant change on 3.3 is using protobuf 3.7.1

  *   HADOOP-16557<https://issues.apache.org/jira/browse/HADOOP-16557> | Major 
| [pb-upgrade] Upgrade protobuf.version to 3.7.1
Will this cause any compatibility issue when upgrading from Hadoop 3.2.x to 
3.3? And will rolling upgrade be supported in this upgrade case?

Thanks,
Jason