On devices where non-system users are not allowed to dream, disable the
screen saver setting when the current user is not the system user.
Bug: 213906883
Test: atest ScreenSaverPreferenceControllerTest
Test: Manually with the following steps:
Step 1: On a device with the config setting
config_dreamsOnlyEnabledForSystemUser set to false, make sure that
non-system users can still access the screen saver setting.
Step 2: On a device with the config setting
config_dreamsOnlyEnabledForSystemUser setting is set to true, make sure
that non-system users can not access (or see) the screen saver setting.
Step 3: Make sure that system users can still see the screen saver
setting on a device where config_dreamsOnlyEnabledForSystemUser is set
to true.
Change-Id: I7e167ed5a1ea183c725ba89a57b8d0b372064b82
640247eb58