trial_request: Trial Request uses HostingSubscription Property Sheet

Trial Request should save if the request if for an slave instance or not, for this we use root_slave.

master/bt5/slapos_trial_request/PortalTypePropertySheetTemplateItem/property_sheet_list.xml

 <property_sheet_list>
  <portal_type id="Trial Request">
+  <item>HostingSubscription</item>
   <item>Organisation</item>
   <item>Reference</item>
   <item>Task</item>

master/bt5/slapos_trial_request/bt/template_portal_type_property_sheet_list

+Trial Request | HostingSubscription
 Trial Request | Organisation
 Trial Request | Reference
 Trial Request | Task