CDAP-640 - Metrics Increase RunId max Entries 

This PR is to increase the for max entries for runId in Metrics Entity Table from (2^16) to (2^32) 

While testing this, we figured an issues with our levelDB getRow implementation, where the limit was ignored and due to that we were scanning the entire table for a simple incrementAndGet. This PR contains the fix for that as well.

https://issues.cask.co/browse/CDAP-640
just do entity.paddedEncodeRunId(runId, padding);