get_platform() returns string as "cray" if it's a actual Cray cluster and returns string as "craysim" if it's a Cray simulator.
I have updated and mentioned these two string values in doc.
Talking about three interfaces, if test user wants to just check whether the platform is Cray or Cray simulator then he can just call "is_cray()" or "is_cray_simulator()" for any specified system in a cluster, which will return true or false. User doesn't need to remember strings ('cray', 'craysim') and compare it, which will simplify users job in my opinion. Also in very rare case if we change these strings internally then it will affect at all places.