Make 'cache is clean' message debug

(Bitbake rev: 92637a355d55cb66de91b4314bc0e7cf1ac64ade)

Signed-off-by: Chris Larson <chris_larson@mentor.com>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>

bitbake/lib/bb/cache.py

@@ -328,7 +328,7 @@ class Cache:
             return
 
         if self.cacheclean:
-            logger.info("Cache is clean, not saving.")
+            logger.debug(2, "Cache is clean, not saving.")
             return
 
         version_data = {}