make it impossible to skip past a provisioning proxy step without run results

It is now not possible anymore to 'skip past' the workflow step where you have to wait for the provisioning proxy to return its results.

gso/services/provisioning_proxy.py

@@ -14,6 +14,7 @@ from orchestrator.forms import FormPage, ReadOnlyField
 from orchestrator.forms.validators import Accept, Label, LongText
 from orchestrator.types import UUIDstr, State, strEnum
 from orchestrator.utils.json import json_dumps
+from pydantic import validator
 
 from gso import settings
 from gso.products.product_types.device import DeviceProvisioning
@@ -179,6 +180,13 @@ def await_pp_results(subscription: SubscriptionModel,
         pp_run_results: dict = None
         confirm: Accept = Accept('INCOMPLETE')
 
+        @validator('pp_run_results', allow_reuse=True, pre=True, always=True)
+        def run_results_must_be_given(cls, run_results):
+            if run_results is None:
+                raise ValueError('Run results may not be empty. '
+                                 'Wait for the provisioning proxy to finish.')
+            return run_results
+
     result_page = yield ProvisioningResultPage
 
     return result_page.dict()