binman: Allow timeout to occur in the image or its section

At present testThreadTimeout() assumes that the expected timeout happens
first when building the section, but it can just as easily happen at the
top-level image. Update the test to cope with both.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Marek Behún <marek.behun@nic.cz>