Implement DevicePolicyManager.setSystemSettings.

b/67627818
Bug: 67627818
Test: runtest -x services/tests/servicestests/src/
com/android/server/devicepolicy/DevicePolicyManagerTest.java

design doc: https://docs.google.com/document/d/
1rvEg5jE3lMhjH-OA0iTLBUY2opM96fg7BrP81MoPnmg/edit#

Change-Id: If5f5c280957085480872f2d59ed59309cf288145
9 files changed