Fix SettingsDumpServiceTest

SettingsDumpService behavior changed in
Change I9d7fe2e763b9e5840ee76c5eb00bc88288e7ee41

After behavior changed, PrintWriter was wrapped in IndentingPrintWriter,
it's harder to mock the PrintWriter, so check the result directly.

Fix: 280068083
Test: RobolectricTest
Change-Id: I92a7b931c93df4cd9e9c3e47b91a9750df936f15