sim: testsuite: allow tests to declare expected exit status

sim: testsuite: allow tests to declare expected exit status

Some tests want to verify they can control the exit status, and
allowing any non-zero value would allow tests to silently fail:
if it crashed & exited 1, or forced all non-zero to 1, then we
wouldn't be able to differentiate with a test exiting with a
status like 47.

Extend the test harness to allow tests to declare their expected
exit status that would be defined as a "pass".  This requires a
small tweak to the sim_run API to return the status directly, but
that shouldn't be a big deal as it's only used by sim code.