sim: Return exit status from sim run
sim: Return exit status from sim run

Instead of just printing a message, return an exit status so that
scripts running the sim can more easily tell if the tests passed.

Jira: MCUB-45

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