Disable factory reset for secondary users

Search in Settings makes it possible to find the factory reset screen.
Disable the search index in PrivacySettings so that backup and reset
keywords don't get indexed for secondary users.
Also add additional safeguards for other entry points such as public
intents, so that the backup/reset screen does not show any options.

Bug: 18076086
Change-Id: Ie5135fbf4084038c99947a1a107ab4758f0c15a9