ALLOW_RULES_IN_PRODUCT_CONFIG

If ALLOW_RULES_IN_PRODUCT_CONFIG is set, pass it to kati via
.KATI_ALLOW_RULES, to issue warnings or errors about rules
during product configuration.

Test: CHECK_FOR_RULES=true ./build/make/tools/product_config/test.sh
Test: ALLOW_RULES_IN_PRODUCT_CONFIG=error m nothing
Test: ALLOW_RULES_IN_PRODUCT_CONFIG=warning m nothing
Test: m nothing
Change-Id: I35dd9ffe4ec71f97beaa8b8a2f10d80502088af2