Add a new vertex to an existing graph of vertices and edges.

[Muniraju Pulipalyam]

I have an existing graph with 5000 vertices and 80000 edges. The vertices are 
in 4 chunks. When I try to use verticesBuilder and create 5001st vertex to add 
to existing collection, it is overriding existing vertex chunks. I also tried 
WriteTable, but can't find a way to append. I saw samples on mid-level and 
high-level writers and other samples where new files are created in /tmp 
folder. I want to append a vertex to an existing vertex collection. What API 
can I use to append a vertex to vertex collection and write back to file?

Thanks.