Start waffle namespace deprecation

By explicitly importing the legacy namespace classes, we make it clear
that we are using soon-to-be-deprecated classes. We will then be able to
start removing the legacy classes, one module at a time.

common/lib/xmodule/xmodule/seq_module.py

@@ -23,7 +23,7 @@ from xblock.core import XBlock
 from xblock.exceptions import NoSuchServiceError
 from xblock.fields import Boolean, Integer, List, Scope, String
 
-from edx_toggles.toggles import WaffleFlag
+from edx_toggles.toggles import LegacyWaffleFlag
 from openedx.core.lib.graph_traversals import traverse_pre_order
 
 from .exceptions import NotFoundError
@@ -48,7 +48,7 @@ class_priority = ['video', 'problem']
 #  `django.utils.translation.ugettext_noop` because Django cannot be imported in this file
 _ = lambda text: text
 
-TIMED_EXAM_GATING_WAFFLE_FLAG = WaffleFlag(
+TIMED_EXAM_GATING_WAFFLE_FLAG = LegacyWaffleFlag(
     waffle_namespace="xmodule",
     flag_name=u'rev_1377_rollout',
     module_name=__name__,