bitbake: cooker/cookerdata/event: Improve class handlers management

Similarly to the execution context changes, establish better lifetime
management API of the class event handlers.

(Bitbake rev: 54e35a6cceead9521f8b1dacd48e55064e85c8bd)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/cookerdata.py

@@ -174,6 +174,7 @@ class CookerDataBuilder(object):
         self.tracking = params.tracking
 
         bb.utils.set_context(bb.utils.clean_context())
+        bb.event.set_class_handlers(bb.event.clean_class_handlers())
         self.data = bb.data.init()
         if self.tracking:
             self.data.enableTracking()