Yaml safe_load does not handle exceptions. Closes #2051

celery/backends/base.py

@@ -43,7 +43,7 @@ from celery.utils.serialization import (
 
 __all__ = ['BaseBackend', 'KeyValueStoreBackend', 'DisabledBackend']
 
-EXCEPTION_ABLE_CODECS = frozenset(['pickle', 'yaml'])
+EXCEPTION_ABLE_CODECS = frozenset(['pickle'])
 PY3 = sys.version_info >= (3, 0)
 
 logger = get_logger(__name__)