SetupWizard: Fixup backup/restore for Marshmallow.

  Since Marshmallow broke the ability to utilize complex
  matrix queries against the SettingsProvider because it
  is now backed by XML, rewrite the logic for the backup
  enabled flag to work within the new constraints.

Change-Id: I8ad993564184fa14b5a3267689c69af2f7e8638e
TICKET: CYNGNOS-2233
(cherry picked from commit 0d83f7c0)