slapos_cloud: set compute node default allocation scope to open by default

master/bt5/slapos_cloud/WorkflowTemplateItem/portal_workflow/compute_node_slap_interface_workflow/script_ComputeNode_approveRegistration.py

 compute_node = state_change['object']
 portal = compute_node.getPortalObject()
 compute_node.edit(
+  allocation_scope='open',
   upgrade_scope='auto',
   capacity_scope='open'
 )