Fix xml loading for managed services

Noticed while adding a shell cmd to toggle notification assistants,
which is also included

Bug: 62263757
Test: runtest systemui-notification
Change-Id: I9bc0ee857abb8b9f60ab18ad740ca0a3b7d754ff
(cherry picked from commit 88facd4d9ac18630e4cc44db22b88b4ba26e775a)
8 files changed