Reduce logging levels for several client log messages

[sfitts]

Version -- 3.5.1

The logging levels for some things are pretty verbose. For example, line 174 of MqttClientImpl uses an "error" log level for an exception that will be given to the connection handler (so the caller will get the error and can decide if it wants to scream about it -- we don't).

In the same place successful connections print an "INFO" log (at line 179).

In general I'd prefer if Vert.x logging was DEBUG and below except in extreme circumstances.

[vietj]

I agree with you.

one practice I found is to log only the message of these errors (some are expected) but log the full trace if debug is enabled

[vietj]

@ppatierno