generic timeout error when 'is_ssl' param not set for an mqtt service that requires it

[jersu11]

This was discovered while debugging a connection issue with the adafruit_aws_iot library. When the MQTT client is instantiated without the is_ssl param for a service that requires ssl, the MQTT client will attempt retries and eventually fail with an error that is perhaps too generic.

MMQTTException('Repeated connect failures',)

[justmobilize]

investigating