cbc-pillowfight not backwards compatible when using auth

With the RBAC additions in 5.0, we now need to supply pillowfight with credentials (-u user -P password).  However, this is not compatible with pre 5.0 installations and results in an error:

Operation(s) failed: [0x2] Authentication failed. You may have provided an invalid username/password combination

This makes it much harder to script a load generation command because the end-user needs to detect which version of the server is being accessed.  

Can the library make this check ahead of time and only send credentials when needed (5.0+) and not when not needed (<5.0)?