CAMEL-6869  Support reconnection when broker goes down

- Add Spring DSL test
- Try to fix CAMEL-6869: https://issues.apache.org/jira/browse/CAMEL-6869

When the broker is not available, and Camel starts:
   - If Producer starts, the connection will be lazily opened on message sending
   - If Consumer starts, a background task is started, waiting to register the message listener as soon as the broker is available

When Camel is started and the broker is stopped, or becomes unavaible:
   - Tuning the requestedHeartbeat, networkRecoveryInterval, automaticRecoveryEnabled on connectionfactory should be enough

Comment if you think the fix is not satisfactory or if you see a better way to handle broker unavailability.