slapos_subscription_request: use the same hosting subscription periodicity per user

Ensure all invoices for one user will be created at the same date.

Ensure all users do not use the same periodicity, to NOT generated all system invoices on the same date.

master/bt5/slapos_subscription_request/SkinTemplateItem/portal_skins/slapos_subscription_request/SubscriptionRequest_createOpenSaleOrder.py

@@ -22,8 +22,12 @@ if hosting_subscription.getPeriodicityHour() is None:
 if hosting_subscription.getPeriodicityMinute() is None:
   edit_kw['periodicity_minute_list'] = [0]
 if hosting_subscription.getPeriodicityMonthDay() is None:
-  start_date = hosting_subscription.HostingSubscription_calculateSubscriptionStartDate()
-  start_date = getClosestDate(target_date=start_date, precision='day')
+  # do not use the same date for every users
+  # to prevent overload of the server at this date
+  # Use the person creation date for now, as this document is always accessible
+  # without relying on portal_catalog / serialize
+  customer_person = subscription_request.getSourceSectionValue()
+  start_date = getClosestDate(target_date=customer_person.getCreationDate(), precision='day')
   while start_date.day() >= 29:
     start_date = addToDate(start_date, to_add={'day': -1})
   edit_kw['periodicity_month_day_list'] = [start_date.day()]
@@ -39,6 +43,8 @@ current_date = getClosestDate(target_date=hosting_subscription.getCreationDate()
 next_period_date = hosting_subscription.getNextPeriodicalDate(current_date)
 
 if subscription_request.getQuantityUnit() == 'time/month':
+  # This start_date calculation ensures the first invoices period
+  # will be merged in the user monthly invoice
   start_date = addToDate(next_period_date, to_add={'month': -1})
   assert hosting_subscription.getNextPeriodicalDate(start_date) == next_period_date
 else: