Stability test for call with and without backups and repartitionings

Makes sure that the system is able to deal with repartitionings while doing operations with and without backups.
made the get/put operations multithreaded to cause more load
Merge pull request #1180 from pveentjer/improvement/3.x/repartitioning-stresstests

Stability test for call with and without backups and repartitionings