Read "Database Status" page connection information from cluster config if present

Summary:
Fixes T11043. This page was still reading the old information directly instead of going through the cluster-aware stuff.

Have it ask the cluster-aware stuff for information instead.

Test Plan:

• Nuked MySQL on localhost.
• Configured cluster hosts.
• Loaded "Database Status" page -- worked after patch.
• Grepped for any remaining mysql.configuration-provider stragglers, came up empty.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11043

Differential Revision: https://secure.phabricator.com/D15982