Load /prop.default in recovery mode

Bug: 37815285
Bug: 62525809
Test: Tested with ag/2398663 and ag/2400523. Booted pixel phones,
      checked the location of prop.default, verified the symlink,
      checked a few properties via adb shell and manually tested
      a few apps.
      Booted to recovery and ran 'adb sideload' successfully.
Change-Id: I034b700fcd60b0104873131e94864b16ef4bd9f6