Handle refTable values with setkey()

For columns like QoS.queues where we have a map containing refTable
values, assigning w/ __setattr__ e.g. qos.queues={1: $queue_row}
works, but using using qos.setkey('queues', 1, $queue_row) results
in an Exception. The opdat argument can essentially just be the
JSON representation of the map column instead of trying to build
it.

Signed-off-by: Terry Wilson <twilson@redhat.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

python/ovs/db/idl.py

@@ -1567,10 +1567,9 @@ class Transaction(object):
                     for col, val in row._mutations['_inserts'].items():
                         column = row._table.columns[col]
                         if column.type.is_map():
-                            opdat = ["map"]
                             datum = data.Datum.from_python(column.type, val,
                                                            _row_to_uuid)
-                            opdat.append(datum.as_list())
+                            opdat = self._substitute_uuids(datum.to_json())
                         else:
                             opdat = ["set"]
                             inner_opdat = []