fix encoding of MetadataResponse with version >= 2
fix encoding of MetadataResponse with version >= 2

ThrottleTimeMs and ClusterID have been added to decode(), but apparently
encode() was forgotten. This causes errors in tests, if versions >= 2 are used.

DataDog/sarama,Shopify/sarama,Shopify/sarama,DataDog/sarama,VividCortex/sarama,VividCortex/sarama