Skipping call to generate default machine ID when it's not required

FDB uses a shared memory file to generate a random default machine ID, and uses that as the machineid and zoneid in the locality if none are provided explicitly. If both are provided, it still generates the machine ID, but doesn't do anything with it. This is slightly wasteful, and also creates a dependency on shared memory that doesn't exist elsewhere in the system. This could cause problems in environments where shared memory is disabled or misconfigured. Can we defer the generation of the machine ID until it is required?