Create a sample-boku-bango.py script (bug 998048)

- Create a generic seller, product
- Create a bango seller, product
- Start a bango transaction
- Create a boku seller, product
- Start a boku transaction
- Retrieve the generic product, check that both providers info is included
Merge pull request #233 from JaredKerim-Mozilla/998048

Create a sample-boku-bango.py script (bug 998048)