* Since A/B addon.d scripts are going to need to do things in a
specific way or things could go horribly wrong for a user, let's
introduce versioning so that scripts can claim to be compatible.
* A script can denote it is compatible with addon.d version 2 by
adding: "# ADDOND_VERSION=2" somewhere in its script.
* Only A/B will require version 2 scripts for now, and version 2
scripts will still run on non-A/B. Additionally if a script does
not explicitly denote its version, assume its version 1.
* Version 1: The same old scripts we've always used. We cannot assume
these will all work with A/B backuptools.
* Version 2: Scripts that denote they are compatible with version 2
must be aware of the fact that A/B devices will run this
script for a rom, during a seamless update, mounted at
/postinstall. The best way to ensure compatibility would
be to use the pre-designated functions found in the
backuptool[,_ab].functions scripts.
Change-Id: I5573018dabd21bb64c7c964e2081806072a75243
524fe03bfb