update.py: improve handling of machine descriptions
update.py: improve handling of machine descriptions

Fall back to NAME if DESCRIPTION is not specified and remove more
preamble from the string.

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

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