MB-9933: Make option and help consistent for setting-autofailover

Change-Id: I5ba02985d12c7f410a03c91a5629f756dc18ae64
Reviewed-on: http://review.couchbase.org/35731
Reviewed-by: Bin Cui <bin.cui@gmail.com>
Tested-by: Bin Cui <bin.cui@gmail.com>