buildman: Translate more strings to latin-1

When writing out some of our results we may now have UTF-8 characters
in there as well.  Translate these to latin-1 and ignore any errors (as
this is for diagnostic and given the githash anything else can be
reconstructed by the user.

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>