Add keys to all Preferences on the Managed device info page

In order to be able to hide the page from search results, all Preferences
(and PreferenceCategories) must have android:keys.

Bug: 62285529
Test: The Settings framework will have a test that ensure each Preference
Test: has a key from O-DR onward

Change-Id: I1e41ce6f8b9f90155ef92354b9268e9e720e1e73