GUACAMOLE-527: Add error logging for known host checks.
GUACAMOLE-527: Add error logging for known host checks.

mike-jumper/incubator-guacamole-server,apache/guacamole-server,glyptodon/guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,apache/guacamole-server,mike-jumper/incubator-guacamole-server,glyptodon/guacamole-server,mike-jumper/incubator-guacamole-server,glyptodon/guacamole-server