[FEATURE] Create test for db auction

# Changelog:
    Add a part of test (test of DB auction)
# Motivation:
    I developed an one auction 10 years ago. I want to share the experience.
# Usage guide:
    Code for creating the table can be used in node/setup_db.py
# Roadmap:
* test_auction.py (DB,node/auction,FrontEnd api,protocol, etc.),
* DB(node/setup_db.py), 
* node/auction.py, 
* etc.

We now have [package structure](https://github.com/OpenBazaar/OpenBazaar/pull/665) installed, so you needn't have to mess with `sys.path` for your imports to succeed. Just import the modules that you want.