Fix encoding errors when hashing XML

We occasionally get UnicodeEncodeErrors from these two places,
because the XML is a Unicode string, and is implicitly encoded to ascii.

common/lib/xmodule/xmodule/error_module.py

@@ -87,7 +87,7 @@ class ErrorDescriptor(ErrorFields, JSONEditingDescriptor):
                 # but url_names aren't guaranteed to be unique between descriptor types,
                 # and ErrorDescriptor can wrap any type.  When the wrapped module is fixed,
                 # it will be written out with the original url_name.
-                name=hashlib.sha1(contents).hexdigest()
+                name=hashlib.sha1(contents.encode('utf8')).hexdigest()
             )
 
         # real metadata stays in the content, but add a display name

common/lib/xmodule/xmodule/modulestore/xml.py

@@ -108,7 +108,8 @@ class ImportSystem(XMLParsingSystem, MakoDescriptorSystem):
                         orig_name = orig_name[len(tag) + 1:-12]
                     # append the hash of the content--the first 12 bytes should be plenty.
                     orig_name = "_" + orig_name if orig_name not in (None, "") else ""
-                    return tag + orig_name + "_" + hashlib.sha1(xml).hexdigest()[:12]
+                    xml_bytes = xml.encode('utf8')
+                    return tag + orig_name + "_" + hashlib.sha1(xml_bytes).hexdigest()[:12]
 
                 # Fallback if there was nothing we could use:
                 if url_name is None or url_name == "":