'vendor_available: *' will not create product variant

With this patch, `vendor_available: true` will no longer creates
product variant. Instead, modules need to set `product_available:
true` if they have to be available to product vanriant.
If both properties are defined for VNDKs, they must have the same
values.

Bug: 150902910
Test: m nothing
Change-Id: I28fb6886e6114583227a31151136627c8516ac9c