move suspended problems list to advanced settings

Moved the list of suspended problems to advanced settings (ie
policy.json) instead of defining them in the <randomize> tag within the
course xml. This avoids potentially destroying student state and makes
it easier for course admins to add/remove suspended problems. Course
admins can now define *all* suspended problems in one place simply by
listing them in the 'Advanced Settings' page of the studio web
interface.

common/lib/xmodule/xmodule/modulestore/inheritance.py

@@ -5,7 +5,7 @@ Support for inheritance of fields down an XBlock hierarchy.
 from datetime import datetime
 from pytz import UTC
 
-from xblock.fields import Scope, Boolean, String, Float, XBlockMixin, Dict, Integer
+from xblock.fields import Scope, Boolean, String, Float, XBlockMixin, Dict, Integer, List
 from xblock.runtime import KeyValueStore, KvsFieldData
 
 from xmodule.fields import Date, Timedelta
@@ -86,6 +86,11 @@ class InheritanceMixin(XBlockMixin):
               "If the value is not set, infinite attempts are allowed."),
         values={"min": 0}, scope=Scope.settings
     )
+    suspended = List(
+        help="A list of problem url_name's to exclude from the list of "
+        "choices in the randomize XModule",
+        scope=Scope.settings
+    )
     proctor_url = String(
         help="URL of proctor server",
         scope=Scope.settings

common/lib/xmodule/xmodule/randomize_module.py

@@ -18,6 +18,7 @@ class RandomizeFields(object):
     choice = String(help="Which random child was chosen",
                     scope=Scope.user_state)
     history = List(help="History of randomize choices", scope=Scope.user_state)
+    suspended = List(help="Suspended problems", scope=Scope.settings)
 
 
 class RandomizeModule(RandomizeFields, XModule):
@@ -50,8 +51,6 @@ class RandomizeModule(RandomizeFields, XModule):
         xml_attrs = self.descriptor.xml_attributes or []
         self.use_randrange = self._str_to_bool(xml_attrs.get('use_randrange', ''))
         self.no_repeats = self._str_to_bool(xml_attrs.get('no_repeats', ''))
-        suspended = xml_attrs.get('suspended', '').split(',')
-        self.suspended = [i.strip() for i in suspended if i.strip()]
         self.pick_choice(use_randrange=self.use_randrange,
                          no_repeats=self.no_repeats, suspended=self.suspended)