Raise a "you should upgrade your storage" note for a missing database

Summary: We raise an improved exception for missing tables/columns, but not databases.

Test Plan: Hit a "no such database error", got a better error message pointing me at storage upgrades.

Reviewers: btrahan, jungejason

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D2429