Previous logging configuration should be checked against `logging.root.handlers`. Refs #3155

```python
>>> import logging
>>> logging.root.handlers
[]
>>> logging.basicConfig(level=logging.WARNING)
>>> logging.root.handlers
[<logging.StreamHandler object at 0xb70021cc>]
>>> logging.root.level
30
>>> import salt.client
>>> logging.root.level
30
>>> logging.root.handlers
[<logging.StreamHandler object at 0xb70021cc>]
>>> import salt.log
>>> salt.log.setup_console_logger()
>>> logging.root.handlers
[<logging.StreamHandler object at 0xb70021cc>, <logging.StreamHandler object at 0xb70336ec>]
>>> 
```