Get giraph tests working again by adding a FeatureOverride annotation.

Giraph tests weren't running because giraph doesn't support features for directly adding vertices/edges.  Those features were recently added to all tests that needed them.  The FeatureOverride annotation allows a Graph to override its own features for purposes of tests as long as the graph has some other way to support the test.  In giraph's case that means it must have its own way to handle the @LoadGraphWith function.