Continue on bad database configuration from select scripts

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