Fix multiproduct_kati product list

When the config loading was changed to using AndroidProducts.mk lists
from soong_ui instead of finding them itself, multiproduct_kati stopped
being able to find all the products. Move the finder initialization
earlier so that we can dump the full list.

Test: build/soong/build_test.bash -only-config
Test: forrest runs of every downstream build_test
Change-Id: I085d40f9008a47b850783499365977a0ff70ac66