This is so that we can split the build_test build on large branches into
multiple builds, each testing a subset of the products.
Test: m blueprint_tools (runs the go unit tests)
Test: build/soong/build_test.bash --only-config
vs
Test: build/soong/build_test.bash --only-config --shard-count=2
Test: build/soong/build_test.bash --only-config --shard-count=2 --shard=2
Change-Id: I40ccc1aa477bc0ffa74ff564d155068509be18f0
9609ad9c21