test: Check exit status in run_and_log_expect_exception()

This check was missed. Add it and make the message more verbose.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reported-by: Tom Rini <trini@konsulko.com>
Fixes: 9e17b034 (test/py: Provide a way to check that a command fails)
2 files changed