shards_and_config_return_last_committed_optime.js shouldn't assume opTime in response equals opTime in metadata

shards_and_config_return_last_committed_optime.js runs replSetGetStatus and asserts the last committed opTime timestamp in the response's body equals the last committed opTime metadata field in the response, which may not be true if the last committed opTime advances between executing the command and computing its metadata. The test should assert the last committed opTime in the metadata is >= the opTime in the response body instead.