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
Change-Id: If9390e2b9a0a82c7a374daa260e3496cffaa6d2a
2 files changed