util: add bool_or_none function
util: add bool_or_none function

A version of str_to_bool that tolerates None argument
(returns None if argument is None, otherwise converts
to boolean)

Signed-off-by: Ilija Hadzic <47a09d4a4430975766160361f65fc72633be50b6@gmail.com>

ihadzic/jim,ihadzic/jim,ihadzic/jim