MB-5904 remove passwords from babysitter logs

- MOXI_SASL_PLAIN_PWD from ns_child_ports_sup logging

Change-Id: I14547605d4d6a8550ec7f0898ea6f1bd81f9f699
Reviewed-on: http://review.couchbase.org/28042
Tested-by: Artem Stemkovski <artem@couchbase.com>
Reviewed-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>