erp5_oauth2_resource: Switch upgrader constraint from id to meta_type

Duplicating the id is bad. Checking the meta_type is not perfect, but it
is one step better.

bt5/erp5_oauth2_resource/SkinTemplateItem/portal_skins/erp5_oauth2_resource/ERP5Site_checkOAuth2ResourceServerPostUpgradeConsistency.py

 error_list = []
-# XXX: duplicates a value from product/ERP5/ERP5Site.py
-# It would be better to check plugin class, and not just its id.
-plugin_id = 'erp5_oauth2_resource'
 user_folder = context.getPortalObject().acl_users
-if plugin_id not in user_folder:
-  # XXX: does not check plugin personalities registration, but these are
-  # automaticaly done on plugin creation, so unregistering them should be
+for plugin_value in user_folder.objectValues():
+  # Note: does not check plugin personalities registration, but these are
+  # automaticly done on plugin creation, so unregistering them should be
   # a conscious admin action, that should likely be respected.
+  # XXX: testing the type would be nicer than testing the meta_type attribute
+  if getattr(plugin_value, 'meta_type', None) == 'ERP5 OAuth2 Resource Server Plugin':
+    break
+else:
   error_list.append('PAS plugin %r does not exist' % (plugin_id, ))
   if fixit:
     user_folder.manage_addProduct['ERP5Security'].addERP5OAuth2ResourceServerPlugin(