windeployqt: add a -dry-run option to simulate deployment

For some use cases, only output (not deployment) may be required. This
adds an option to only simulate deployment, without copying any files.

Change-Id: I5ed6fcfd802255f6c8d9091f547a1b64a4a614e5
Reviewed-by: Friedemann Kleint <Friedemann.Kleint@digia.com>