run.py: allow to specify image path

This will be needed my mkzfs.py

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
Fix make mode=debug

We should pass the image path to run.py

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>
run.py: simplify

Signed-off-by: Tomasz Grabiec <tgrabiec@cloudius-systems.com>