LP#1341687 listeners log/drop XMPP error msgs

The most common form of XMPP error messages are "bounced" messages, i.e.
those where the recipient is not available.  Instead of passing these
useless and confusing messages down to a drone for processing, log the
error in the listener and drop the message.

Signed-off-by: Bill Erickson <berick@esilibrary.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>