update.py: fix Ctrl+C handling during layer update
update.py: fix Ctrl+C handling during layer update

We do not want to continue on to the next layer on Ctrl+C.

Signed-off-by: Paul Eggleton <737d4dae46a541673d7bf4e0d5b32714b16528d8@linux.intel.com>

bartosh/layerindex-web,bartosh/layerindex-web,bartosh/layerindex-web