libweave: Don't check error messages in unittests Error code checks should be enough. BUG=none TEST='FEATURES=test emerge-gizmo buffet' Change-Id: I8c9ec8cd1c368bc46f247162e7a77be6e1f869fa Reviewed-on: https://chromium-review.googlesource.com/289642 Trybot-Ready: Vitaly Buka <vitalybuka@chromium.org> Tested-by: Vitaly Buka <vitalybuka@chromium.org> Reviewed-by: Alex Vakulenko <avakulenko@chromium.org> Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>