Add unit test for gremlin interface.
Add unit test for gremlin interface.

mogui/pyorient,orientechnologies/pyorient,mogui/pyorient,Ostico/pyorient,orientechnologies/pyorient,Ostico/pyorient,lebedov/pyorient,ziyangzeng/pyorient,ziyangzeng/pyorient,lebedov/pyorient