tools: ynl: add more info to KeyErrors on missing attrs

When developing specs its useful to know which attr space
YNL was trying to find an attribute in on key error.

Instead of printing:
 KeyError: 0
add info about the space:
 Exception: Space 'vport' has no attribute with value '0'

Reviewed-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20230814205627.2914583-4-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>