ota: Remove cruft we don't care about

Skip the date check (downgrade to your content), and don't include
recovery in otapackages.
5.0.0 update: We want the recovery patchstuff back
fix up ota_from_target_files symlink detection.
Add otapackage support for backuptool

Change-Id: I512554c579d444067cd3ccbb0e6946a5eb6bc964a