bitbake: Fix default function parameter assignment to a list

With python you should not assign a list as the default value of a
function parameter - because a list is mutable, the result will be that
the first time a value is passed it will actually modify the default.
Reference:

http://docs.python-guide.org/en/latest/writing/gotchas/#mutable-default-arguments

(Bitbake rev: 7859f7388f2e3f675d0e1527cfde18625f36f637)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/bb/event.py

@@ -176,7 +176,7 @@ def fire_from_worker(event, d):
     fire_ui_handlers(event, d)
 
 noop = lambda _: None
-def register(name, handler, mask=[]):
+def register(name, handler, mask=None):
     """Register an Event handler"""
 
     # already registered
@@ -389,7 +389,7 @@ class DiskFull(Event):
 class NoProvider(Event):
     """No Provider for an Event"""
 
-    def __init__(self, item, runtime=False, dependees=None, reasons=[], close_matches=[]):
+    def __init__(self, item, runtime=False, dependees=None, reasons=None, close_matches=None):
         Event.__init__(self)
         self._item = item
         self._runtime = runtime