slapos_subscription_request: Add erp5_commerce as dependency

When the testnode installing slapos_subscription_request, it reports:

2019-10-08 19:09:59,997 INFO     runTestSuite: Adding erp5_web_renderjs_ui business template ... (imported in 2.513s) done (21.342s)
2019-10-08 19:09:59,997 INFO     runTestSuite: Adding slapos_subscription_request business template ... (imported in 2.692s) Traceback (most recent call last):
.....
2019-10-08 19:10:00,008 INFO     runTestSuite: ValueError: "commerce_validation_workflow" is not a workflow ID

I found the commerce_validation_workflow is inside erp5_commerce bt. So I add erp5_commerce as the dependency of slapos_subscription_request.