buildman: Change the exit codes

The current exit codes of 128 and 129 are useful in that they do not
conflict with those returned by tools, but they are not actually valid.
It seems better to pick some codes which work with 'bit bisect run'.

Update them to 100 (for errors) and 101 (for warnings).

Signed-off-by: Simon Glass <sjg@chromium.org>
3 files changed