Eng 12931 remove mockito dependency in pro (#4934)
Eng 12931 remove mockito dependency in pro (#4934)

* ENG-12931:
Remove dependency on Mockito in PartitionDRGateway since it should not be incorporated into the release build.

* ENG-12931: Add small comment for debug flag on gateway.

simonzhangsm/voltdb,simonzhangsm/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,VoltDB/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,VoltDB/voltdb,VoltDB/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,VoltDB/voltdb,simonzhangsm/voltdb,simonzhangsm/voltdb,simonzhangsm/voltdb