MB-8974 suppress unnecessary error messages in cbreset_password

- do not display failed attempts to read initargs if one of the
  attempts succeeded
- suppress confusing stderr output from erl shell script on mac

Change-Id: Ibe75411caddb21e209734345ee246a9a85764541
Reviewed-on: http://review.couchbase.org/28606
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>