INT-2474:MessagingGatewaySupport logging upon Exception at warn level

INT-2474:MessagingGatewaySupport logging upon Exception at warn level

* change unnecessary log's level from warning to debug
Actually no: when we `debug()` exception we don't want to emit entire stack trace, just a message:
```
logger.debug("failure occurred in gateway sendAndReceive: " + e.getMessage());
```

Liu, please, follow with **Commit message formatting rules**:
* headline <= 50 symbols
* Jira link over a line after headline
* some description on the matter.

Rework it and repush with 'Amend last commit'