adapt to tinkerpop tests for mysql backend

[zhoney]

1. multi-source vertex-step problem also exists, filter it.
2. mysql not supporting update vertex/edge property leads to using add vertex/edge to update property, which result in bug tx having 'added vertices' when update properties. fixed.
3. multi-thread tx commit not work. Reset mode to auto-commit after batch commit to fix

[zhoney]

This task will be resolved same time with #19