platform/sgi575: run_model script bug fixes and refactoring

Fix bugs related handling of the model binary path, passing the correct
set of model parameters and handling model launch failuers. While at it,
refactor the handling of parameters for handling automated runs.

Change-Id: I4c66a732f58a6e9225048f1e7d80350d51cab6c8
Signed-off-by: Lokesh B V <lokesh.bv@arm.com>