fix raise syntax

This takes a single argument (the error message), not multiple
arguments that get formatted implicitly.

Change-Id: Idfbc913ea9f93820edb7e955e9e4f57618c8cd1b

manifest_xml.py

@@ -514,7 +514,7 @@ class XmlManifest(object):
           raise
         except Exception as e:
           raise ManifestParseError(
-              "failed parsing included manifest %s: %s", (name, e))
+              "failed parsing included manifest %s: %s" % (name, e))
       else:
         nodes.append(node)
     return nodes