Expose a --migrate-processor-state cli flag so that it can be used outside of dataflows deployed by flowlib

[dbkegley]

It would be nice to provide a --migrate-processor-state flag for the cli so that we can use this command without deploying a flow. For example if you just want to migrate state from one nifi instance to a new instance for a single processor.

For example: --migrate-processor-state --nifi-endpoint http://nifi:8080 --zookeeper-connection zookeeper:2181 --zookeeper-root-node /nifi --old <old-processor-uuid> --new <new-processor-uuid>

This would read the state if from the provided nifi-endpoint and serialize the k,v pairs into their binary representation. Then it should set the value of the zookeeper node /nifi/components/<new-processor-uuid> as the value of the serialized state.