Add JDG 6.2 plugin
Various changes in key generators and value checkers:
* CheckDataStage can check data from StressTest (generally), local mode is supported
* PersistentStorageCapable can force memory-only read (used in CheckDataStage)
* StressTestStage.loadAllKeys = in shared mode all nodes should load all keys
* Added key generator for keys that can carry variable amount of random data (mitigating bigger keys)
Background stressors supporting load-only test case