Fix asset locations in water tank swap example

[prasadtalasila]

Question: Are stage1 and stage2 independent?

Suggested changes:

1. Move wt_event.xml to data directory
2. Can the swap (stage2) be changed to evolve stage?

[prasadtalasila]

@gitting-around , can the stage2 commands of the execute script moved into another bash script? If so, please leave a comment with two different bash code snippets that can be used as replacement. Thanks.