Fix some debug logs in httpclient
Fix some debug logs in httpclient

They are supposed to use Debugf as they have a placeholder argument.

dcos/dcos-cli,kensipe/dcos-cli,kensipe/dcos-cli,dcos/dcos-cli,kensipe/dcos-cli,dcos/dcos-cli,dcos/dcos-cli,kensipe/dcos-cli,kensipe/dcos-cli,dcos/dcos-cli