buildman: Support running from an IDE

buildman: Support running from an IDE

Add a flag to allow buildman to behave properly for use from an IDE. This
shows error/warning output on stderr and drops all summary and progress
information.

This should normally only be used when building a single board.

Fix up a confusing comment for GetResultSummary() while we are here, since
we want to use the Outcome object to access the unprocessed error lines
from the build.

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