added fake-saslauthd.rb which mocks saslauthd for easy testing

Change-Id: I92b374ed836f04a80151e53e131eb4bcc3868a65
Reviewed-on: http://review.couchbase.org/43975
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>