Do not return "set" name if not initiated

Startup two 2.6 mongod's, and one 2.8 mongod, all the same replica set. Connect to one of the 2.6 nodes, and try to initialize the replica set. Bash history here: ➜ mongo git:(CAP-1250) ✗ ls /data/db (CAP-1250⚡) mixed_storage_and_version-0 mixed_storage_and_version-1 mixed_storage_and_version-2 mixed_storage_and_version-3 mixed_storage_and_version-4 mixed_storage_and_version-5 mixed_storage_and_version-6 sconsTests ➜ mongo git:(CAP-1250) ✗ mkdir /data/db/mixed_version (CAP-1250⚡) ➜ mongo git:(CAP-1250) ✗ mkdir /data/db/mixed_version/node0 (CAP-1250⚡) ➜ mongo git:(CAP-1250) ✗ mkdir /data/db/mixed_version/node1 (CAP-1250⚡) ➜ mongo git:(CAP-1250) ✗ mkdir /data/db/mixed_version/node2 (CAP-1250⚡) ➜ mongo git:(CAP-1250) ✗ ./mongod-2.6 --dbpath /data/db/mixed_version/node0 --logpath /data/db/mixed_version/node0/mongod.log --logappend --smallfiles --noprealloc --nopreallocj --replSet mixedVersion --fork (CAP-1250⚡) note: noprealloc may hurt performance in many applications about to fork child process, waiting until server is ready for connections. forked process: 12658 child process started successfully, parent exiting ➜ mongo git:(CAP-1250) ✗ ./mongod-2.6 --port 27018 --dbpath /data/db/mixed_version/node1 --logpath /data/db/mixed_version/node1/mongod.log --logappend --smallfiles --noprealloc --nopreallocj --replSet mixedVersion --fork (CAP-1250⚡) note: noprealloc may hurt performance in many applications about to fork child process, waiting until server is ready for connections. forked process: 12670 child process started successfully, parent exiting ➜ mongo git:(CAP-1250) ✗ ./mongod --port 27019 --dbpath /data/db/mixed_version/node2 --logpath /data/db/mixed_version/node2/mongod.log --logappend --smallfiles --noprealloc --nopreallocj --replSet mixedVersion --fork (CAP-1250⚡) note: noprealloc may hurt performance in many applications about to fork child process, waiting until server is ready for connections. forked process: 12682 child process started successfully, parent exiting ➜ mongo git:(CAP-1250) ✗ ./mongo --port 27017 (CAP-1250⚡) MongoDB shell version: 2.8.0-rc1-pre- connecting to: 127.0.0.1:27017/test > rs.initiate({_id: 'mixedVersion', version: 1, members: [{_id: 0, host: 'charlie-macbook-pro:27017'}, {_id: 1, host: 'charlie-macbook-pro:27018'}, {_id: 2, host: 'charlie-macbook-pro:27019'}]}) { "ok" : 0, "errmsg" : "couldn't initiate : member charlie-macbook-pro:27019 is already initiated" } ./mongo --port 27019 (CAP-1250⚡) MongoDB shell version: 2.8.0-rc1-pre- connecting to: 127.0.0.1:27019/test > rs.initiate({_id: 'mixedVersion', version: 1, members: [{_id: 0, host: 'charlie-macbook-pro:27017'}, {_id: 1, host: 'charlie-macbook-pro:27018'}, {_id: 2, host: 'charlie-macbook-pro:27019'}]}) { "ok" : 1 } mixedVersion:OTHER>