misc: Avoid UTF-8 in error messages

misc: Avoid UTF-8 in error messages

While most developers are now using UTF-8 environments, it's
harder to guarantee that error messages will be output to
a multibyte locale. Rather than risking error messages that
get corrupted into mojibake when the user runs qemu in a
non-multibyte locale, let's stick to straight ASCII error
messages, rather than assuming that our use of UTF-8 in source
code string constants will work unchanged in other locales.

Found with:
$ LC_ALL=C git grep -l $'".*[\x80-\xff].*"' origin -- '**/*.[ch]' | cat
origin:hw/misc/tmp105.c
origin:hw/misc/tmp421.c

Reported-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
Reviewed-by: John Snow <jsnow@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20181120203628.2367003-1-eblake@redhat.com>
[lv: added command line to find non ASCII characters]
Signed-off-by: Laurent Vivier <laurent@vivier.eu>