Convert com.twitter.finagle.Addr.Metadata to an instance of ZkMetadata.
Convert com.twitter.finagle.Addr.Metadata to an instance of
ZkMetadata. If ZkMetadata is not present in metadata
,
return the default metadata.
Convert ZkMetadata to an instance of com.twitter.finagle.Addr.Metadata.
Pattern match against metadata
for ZkMetadata and return the
shard ID if it exists.