Use IndentingPrintWriter in DevicePolicyManager

Replace the hardcoded prefix string with IndentingPrintWriter
in various dump() methods in DPMS.

Bug: 138559079
Test: manually diff result of "dumpsys device_policy" before and after
      the change.
Change-Id: Id47c7f877e75071fa17cda48c7277f8aa70dfea5
5 files changed