Secure revisions report a confusing "A generic error occurred in the code review bot"

We posted a secure revision to phabricator with various updates.

Actual Results

• For each update there's an indication that Harbormaster failed remote builds in...
• There's a message at the top of the page that states "A generic error occurred in the code review bot"
• The "Analysis Task" shows as failed.
• Looking at the "Analysis Task" logs, shows there's a line which states Exception: Cannot process private builds

Expected Results

• The build should be flagged as warning, not a failure.
• Code review bot should produce a nice warning message that states are analysis tasks are not run because it is a secure revision.
• It probably doesn't need to notify via email, since this is a permanent state and there's nothing that can be done about it.

Start by tracing how secure revisions reach the Analysis Task and how the Cannot process private builds exception is handled. Verify that secure revisions produce a warning rather than a failure, display a clear message, and do not send an unnecessary email notification.