test-char: split char_file_test

makes it possible to test the existing chardev-file

Signed-off-by: Anton Nefedov <anton.nefedov@virtuozzo.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <1499342940-56739-9-git-send-email-anton.nefedov@virtuozzo.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>