[r=axwalk] Retry replicaset.Initiate

Another attempt at retrying replicaset
initiation. The change I made in
https://codereview.appspot.com/98670045/
does not work well, as the error from
replSetInitiate may be spurious; it is
possible to receive an error despite the
config being written.

https://codereview.appspot.com/102000044/