Don't fail lint builds for "advice"; make lint/unit upload failures louder

Summary:
Ref T8670. Ref T8657.

• When lint only has advice (no warnings/errors), consider it a "passing" build.
• Be a little louder about sendmessage calls failing because this stuff is not totally broken and that makes T8670-related things easier to catch/fix.

Test Plan: Created this revision.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8657, T8670

Differential Revision: https://secure.phabricator.com/D13436