Make SAWarnings go to Sentry as warnings (and not raise an exception).
Make SAWarnings go to Sentry as warnings (and not raise an exception).

Summary:
- This plus D159127 should basically fix T36726.
- Not sure if we have any other Python warnings (it doesn't look like it), but
  those would go to Sentry now too.

Test Plan: None

Reviewers: kylec, paulruan

Reviewed By: paulruan

Subscribers: changesbot

Maniphest Tasks: T36726

Differential Revision: https://tails.corp.dropbox.com/D159151

dropbox/changes,dropbox/changes,dropbox/changes,dropbox/changes