Fix the IsLoopback check
Fix the IsLoopback check

- IsLoopback() is an incorrect check. It will be true if a local proxy (on the same machine as the Kudu server) forwards requests to Kudu as it would be a local connection.
- Instead, checking for the Host header is a better check for mocking APIs

projectkudu/kudu,projectkudu/kudu,EricSten-MSFT/kudu,projectkudu/kudu,EricSten-MSFT/kudu,projectkudu/kudu,projectkudu/kudu,EricSten-MSFT/kudu,EricSten-MSFT/kudu,EricSten-MSFT/kudu