Summary: Ref T11589. Provide a way for scripts to say "just continue if database config fails", and use it in `bin/config` and `bin/storage`.

Test Plan:
  - Broke database config.
  - Ran `bin/config`, worked fine.
  - Ran `bin/storage`, got helpful "set up the database" message.
  - Ran `bin/repository`, got fatal.
  - Ran normal site with valid/invalid config, got proper feedback.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11589

Differential Revision: https://secure.phabricator.com/D16502