[IMP] stock_landed_costs: Convert yml tests to python

addons/stock_landed_costs/__manifest__.py

addons/stock_landed_costs/test/stock_landed_costs.yml

...s/stock_landed_costs/test/stock_landed_costs_rounding.yml

addons/stock_landed_costs/tests/__init__.py

addons/stock_landed_costs/tests/common.py

addons/stock_landed_costs/tests/test_stock_landed_costs.py

...ck_landed_costs/tests/test_stock_landed_costs_rounding.py