fix(api): VM API answers as the VM pages do

- A VM delete reads delete_disk and delete_nvram as booleans from a JSON
  or form body. The view read them as HTML checkboxes from the form body
  only: JSON {"delete_disk": true} kept the disks while reporting success,
  and a form "delete_disk=false" deleted them. Refused options stop
  nothing; the API schema names both options.
- Power on and power cycle of a template answer 409 instead of reporting a
  start that did not happen.
- The VM details leave out the host's ISO images for non-superusers, as
  the VM page does; reading them also refreshed every pool of the host.
- Flavors take values of at least 1, as the web form does, and show their
  id for later changes; a migration needs neither live nor offline; a VM
  create on an unknown compute answers 404 instead of 500.

instances/api/viewsets.py

@@ -26,6 +26,7 @@ from webvirtcloud.serializers import StatusSerializer
 
 from .serializers import (
     CreateInstanceSerializer,
+    DestroyOptionsSerializer,
     FlavorSerializer,
     InstanceDetailsSerializer,
     InstanceSerializer,
@@ -119,7 +120,7 @@ class InstanceViewSet(viewsets.ViewSet):
 
         return Response(serializer.data)
 
-    @extend_schema(responses=StatusSerializer)
+    @extend_schema(request=DestroyOptionsSerializer, responses=StatusSerializer)
     def destroy(self, request, pk=None, compute_pk=None):
         queryset = get_instance(request.user, pk, perm_type="delete")
         if compute_pk is not None and str(queryset.compute_id) != str(compute_pk):
@@ -132,6 +133,8 @@ class InstanceViewSet(viewsets.ViewSet):
         queryset = get_instance(request.user, pk, perm_type="power")
         if compute_pk is not None and str(queryset.compute_id) != str(compute_pk):
             raise Http404()
+        if queryset.is_template:
+            return Response({"status": "Templates cannot be started"}, status=status.HTTP_409_CONFLICT)
         return instance_action_response(poweron, request, pk, "poweron command send")
 
     @extend_schema(request=None, responses=StatusSerializer)
@@ -148,6 +151,8 @@ class InstanceViewSet(viewsets.ViewSet):
         queryset = get_instance(request.user, pk, perm_type="power")
         if compute_pk is not None and str(queryset.compute_id) != str(compute_pk):
             raise Http404()
+        if queryset.is_template:
+            return Response({"status": "Templates cannot be started"}, status=status.HTTP_409_CONFLICT)
         return instance_action_response(powercycle, request, pk, "powercycle command send")
 
     @extend_schema(request=None, responses=StatusSerializer)