wmatrix: more useful error classification

Add several error categories to classify_error.

BUG=chromium:756606
TEST=run live

Change-Id: Iee274ba71c46b235aef75325251747edfbba95fd
Reviewed-on: https://chromium-review.googlesource.com/759410
Commit-Ready: Jacob Kopczynski <jkop@chromium.org>
Tested-by: Jacob Kopczynski <jkop@chromium.org>
Reviewed-by: Xixuan Wu <xixuan@chromium.org>