Hyperdrive config arguments ignored silently when the entry_command is specified

[ozan-oktay]

When the entry_command feature used in conjunction with hyperdrive config, the backend silently ignores the hyperdrive arguments and defaults to the command specified by the user. It basically disables the use of hyperdrive runs and can mislead users. By switching to entry_script option, this issue can be addressed but users should be notified with warnings or run-time errors if it's caused by azureml-core. Thanks

https://github.com/microsoft/hi-ml/pull/909/