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`.

/reviewed-on nexedi/slapos.core!141

master/bt5/slapos_subscription_request/bt/dependency_list

+erp5_commerce
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