Broker Dynamic Configuration fails to resolve variables as per KIP-421

In add/alter new configs for DynamicConfigs it does not go through the KafkaConfig
eg: bin/kafka-configs --bootstrap-server localhost:9092 --entity-type brokers --entity-name 0 --alter --add-config log.cleaner.threads=2
However the bootstrap-server localhost is parsed through the kafkaConfig to create the adminClient but not the log.cleaner.thread. 

As the configs are not parsed using the KafkaConfig if we pass variables in configs they are bot resolved at run time.

In order to resolve the variables in alterConfig/addConfigs flow we need to parse the new configs  using KafkaConfig before they are parsed.