Merge pull request #908 from cpennington/reference-runtime

Replace references to .system

common/lib/xmodule/xmodule/error_module.py

@@ -129,7 +129,7 @@ class ErrorDescriptor(ErrorFields, XModuleDescriptor):
     @classmethod
     def from_descriptor(cls, descriptor, error_msg='Error not available'):
         return cls._construct(
-            descriptor.system,
+            descriptor.runtime,
             str(descriptor),
             error_msg,
             location=descriptor.location,

common/lib/xmodule/xmodule/tests/test_error_module.py

@@ -37,7 +37,7 @@ class TestErrorModule(unittest.TestCase, SetupTestErrorModules):
 
     def test_error_module_from_descriptor(self):
         descriptor = MagicMock([XModuleDescriptor],
-                               system=self.system,
+                               runtime=self.system,
                                location=self.location,
                                _field_data=self.valid_xml)
 
@@ -72,7 +72,7 @@ class TestNonStaffErrorModule(unittest.TestCase, SetupTestErrorModules):
 
     def test_error_module_from_descriptor(self):
         descriptor = MagicMock([XModuleDescriptor],
-                               system=self.system,
+                               runtime=self.system,
                                location=self.location,
                                _field_data=self.valid_xml)