AT:

• using the RuntimeService I can start a process instance by a process definition key and a tenant-id
• if I start a process instance by key without a tenent-id then an exception is thrown if there are multiple deployed process definitions with the given key from different tenant-ids
• if there is only one process definition then the process instance is started
• I can also start a process instance by key and tenant-id using the process instantiation builder auf the runtime service (e.q. createProcessInstanceById(...))