* [PY3] Change log.warn statements to log.warning
log.warn is deprecated in Python 3. This change removes the
occurance of deprecation warnings for using log.warn. For example:
```
17:24:23 [WARNING ] /testing/salt/utils/verify.py:522: DeprecationWarning: The 'warn' method is deprecated, use 'warning' instead
17:24:23 log.warn('Insecure logging configuration detected! Sensitive data may be logged.')
17:24:23
17:24:23 [WARNING ] Insecure logging configuration detected! Sensitive data may be logged.
```
* Tweak unit.utils.verify_test to using warning instead of warn
