Upgrade bazlets to latest stable-2.15 to build with 2.15.12 API
Upgrade bazlets to latest stable-2.15 to build with 2.15.12 API

Change-Id: Ib3999b51dddbe5524c999bbf2c9ca30cd2851039

GerritCodeReview/plugins_admin-console,GerritCodeReview/plugins_admin-console,GerritCodeReview/plugins_admin-console