Add product_available to VNDK snapshots

Using vndkproduct.libraries.txt, add 'product_available' property to
the selected VNDK libraries. If the snapshot does not have
vndkproduct.libraries.txt, create an empty list file and make all
snapshot libraries available to product.

Bug: 174323911
Bug: 150902910
Test: run update.py for various snapshot versions
Change-Id: I3f680abcbf73e3f74c5dad49f57e02de4d87a148
2 files changed