[callVariant] Out edge type not assigned correctly when aligning variant bubbles

[zhuchcn]

This issue was found when running the Backus lab data. When aligning variant bubbles, nodes within the same bubbles will be merged and new out-bond edges must be re-created. In the figure below, the red rectangle is a bubble, and the node in the yellow rectangle is a subgraph out. The node G-ACAGAG...GGACAG-CTTTAA...GCAGAT is created, and out-bond edges are recreated to the downstream G and T. T should be a reference node in it's own subgraph, but because it's upstream subgraph ID gets updated when merging, so the current rule will take this as a variant edge. Consequently, this merged node will have all its out-bond node being "varaint_start" node.