Style: better compliance with community Ruby coding style guide

Summary:
The following points, detected by Rubocop, are improved:

• if !something → unless something
• Ruby 1.9 hash syntax is used
• is_quality? → quality?
• removed extraneous self

Test Plan: Run dashboard, ensure all cards are still available.

Reviewers: dereckson

Differential Revision: http://devcentral.nasqueron.org/D478