Refines JCacheEntryProcessorTest

closes https://github.com/hazelcast/hazelcast/issues/4258

__Source of test failure issue https://github.com/hazelcast/hazelcast/issues/4258__:
If primary and backup entry processors are changing an entry value to two different values on their own nodes, it can not be guaranteed that changed value on backup node is different from primary node, this is because when backup starts to run, cache config may not be there yet, so backup operation fails but data on primary node will eventually be moved to backup.