Skip generate-common-build-props for older devices without /product

Common ro.product properties are always generated for the
product partition, even if it is not present. This was introduced
for the R release with Ia88c8efecb18db9c27baa466e492bfd898b581d3
"Generate product build props always" commit.

It violates CDD requirements for the devices which were released
earlier. Add optional parameter to build-properties which allows to
skip the common properies generation and product partition specific
checks to make sure common properties are not generated for
the devices released before R and without product partition.

Test: manual, build product/etc/build.prop for shipping levels 28, 30
      and for the devices with and without product partitions
Bug: 174677451
Change-Id: Ia3275d7229d0a873e0a4f1d1ea7a25c758c85bb9