Cleanup some clustering rough edges
Summary: Suppress an unhelpful Almanac transaction and document the location of the secret clustering management capability. I thought maybe implementing shouldHide and checking for isCreate would work, but the binding apparently gets created before an interface is bound to it.
Test Plan: Looked at a fresh binding and didn't see "Unknown Object(??)", ran bin/diviner and saw expected output.
Reviewed By: epriestley
Differential Revision: https://secure.phabricator.com/D19917