Copy metrics kafka offset on CDAP upgrade

We are changing the name of the table that stores offset. So in new table offset value becomes 0. But we should use old one - to avoid processing whatever is in kafka from the beginning (which will also cause duplicate processed records).

NOTE: We didn't notice that when doing tests however, which is strange. I.e. nothing is processed twice.. Which would be expected due to this bug. Only explanation - the MetricValue in Kafka topics, its class was changed (package) - that could cause not decoding old metric values.