Do not set default value for any_errors_fatal in Base

Setting default values for FieldAttribute values created in the Base class
prevents the _get_parent_attribute() code from working correctly, as the value
is always non-None.

Related to ansible#22924

lib/ansible/playbook/base.py

@@ -163,7 +163,7 @@ class Base(with_metaclass(BaseMeta, object)):
     _run_once         = FieldAttribute(isa='bool')
     _ignore_errors    = FieldAttribute(isa='bool')
     _check_mode       = FieldAttribute(isa='bool')
-    _any_errors_fatal = FieldAttribute(isa='bool', default=False, always_post_validate=True)
+    _any_errors_fatal = FieldAttribute(isa='bool', always_post_validate=True)
 
     # param names which have been deprecated/removed
     DEPRECATED_ATTRIBUTES = [