NSX|V: improve support of bulk subnets

This addresses a number of issues:
1. The base code would have a open transaction for the bulk
   creation. This would cause problems with the resources created
   for the edges.
2. In the event of one of the subnet created fails then the
   resources created would not be cleaned up.

Change-Id: I3741257a9861e8e27a56772893e624d4c60e2292

vmware_nsx/plugins/nsx_v/plugin.py

@@ -1921,6 +1921,28 @@ class NsxVPluginV2(addr_pair_db.AllowedAddressPairsMixin,
                             "6.2.3 or higher")
                 raise n_exc.InvalidInput(error_message=err_msg)
 
+    def create_subnet_bulk(self, context, subnets):
+
+        collection = "subnets"
+        items = subnets[collection]
+        new_subnets = []
+        for item in items:
+            try:
+                s = self.create_subnet(context, item)
+                new_subnets.append(s)
+            except Exception as e:
+                LOG.error(_LE('Unable to create bulk subnets. Failed to '
+                              'create item %(item)s. Rolling back. '
+                              'Error: %(e)s'), {'item': item, 'e': e})
+                for subnet in new_subnets:
+                    s_id = subnet['id']
+                    try:
+                        self.delete_subnet(context, s_id)
+                    except Exception:
+                        LOG.error(_LE('Unable to delete subnet %s'), s_id)
+                raise
+        return new_subnets
+
     def create_subnet(self, context, subnet):
         """Create subnet on nsx_v provider network.