[DO NOT MERGE] Fix CtsDevicePolicyManagerTestCases not to rely on default ringtone

The default ringtone content is played in testAudioRestriction, but it
could fail on GSI environment if the default ringtone content doesn't
exist on GSI.

This CL fixes not to rely on default ringtone content and use internal
test resource instead.

Bug: 117805558
Bug: 171352281
Merged-In: If9390e2b9a0a82c7a374daa260e3496cffaa6d2a
Change-Id: If9390e2b9a0a82c7a374daa260e3496cffaa6d2a
(cherry picked from commit 359696fee3e62fe6c17da3e035226fccf376b229)