Add aliases for debug levels in rally.log

In Rally, we wrap the standard logging module with our own rally.log
module. This leads to ugle statements like logging.logging.INFO in some
places of Rally, because the logging levels are defined in the standard
logging module, which is, in turn, imported in rally.log.

Change-Id: I89be56592fe1a542e21e105ead17aafbc4b2319f
Merge "Add aliases for debug levels in rally.log"