Safe re-rendering

[sixfeetover]

Support safely re-rendering templates, meaning if an exception is thrown during render, don't overwrite the previously rendered template.

Example situation:

• You have a Rails database.yml file being rendered by Consult.
• In production, your application boots successfully, rendering database.yml.
• The next process that boots throws an exception for whatever reason, and the app fails to launch as a result

Instead of the app failing to launch, we should allow for graceful (and reported - meaning, the error makes it to Rollbar or whatever) failure, so the app can boot with the previously rendered template.

Questions:

1. Should this be configurable on a per-template basis?
2. Should this be the default behavior?