zep2newt.py: use /usr/bin/env when searching for python2
zep2newt.py: use /usr/bin/env when searching for python2

Avoid hardcoding the python2 path by using env python2 instead.

Signed-off-by: Ricardo Salveti <6fd42f733b6586c555e01d4ff3116fc7e73e7330@linaro.org>

tamban01/mcuboot,tamban01/mcuboot,tamban01/mcuboot,ATmobica/mcuboot,utzig/mcuboot,utzig/mcuboot,utzig/mcuboot,ATmobica/mcuboot,ATmobica/mcuboot,utzig/mcuboot,runtimeco/mcuboot,runtimeco/mcuboot,tamban01/mcuboot,runtimeco/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,utzig/mcuboot,ATmobica/mcuboot,runtimeco/mcuboot,tamban01/mcuboot