ENG-5465: Move BalancePartitionsRequest to eng so that the MpScheduler can peak
into the parameters to figure out the partitions involved.
ENG-5465: Create NpProcedureTask in MpScheduler for @BalancePartitions.
ENG-5465: Add fragment IDs for @BalancePartitions' clear index.
ENG-5465: Add comments to explain why NP transactions need to check
partitioning before execution.
ENG-5465: Add comment to explain that @BalancePartitions are not restartable.
Merge branch 'master' into ENG-5465
Merge pull request #1055 from VoltDB/ENG-5465

Eng 5465 Make balance partitions a two partition transaction