Gets a "running" number represented by the cluster info.
Some examples:
1. NumberOfInstances=2, numberOfBackups=0, instanceId=1: RunningNumber = 0.
2. NumberOfInstances=2, numberOfBackups=0, instanceId=2: RunningNumber = 1.
3. NumberOfInstances=2, numberOfBackups=1, instanceId=1, backupId=0: RunningNumber = 0.
4. NumberOfInstances=2, numberOfBackups=1, instanceId=1, backupId=1: RunningNumber = 1.
5. NumberOfInstances=2, numberOfBackups=1, instanceId=2, backupId=0: RunningNumber = 2.
6. NumberOfInstances=2, numberOfBackups=1, instanceId=2, backupId=1: RunningNumber = 3.
Declaration Syntax