buildroot

rabbitmq-server: security bump to version 3.6.6

Fixes a critical authentication vulnerability in the MQTT plugin
(CVE-2016-9877):

MQTT (MQ Telemetry Transport) connection authentication with a
username/password pair succeeds if an existing username is provided but the
password is omitted from the connection request.  Connections that use TLS
with a client-provided certificate are not affected.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>