Add implicit min-sdk if a test uses a main-dex list.

D8 is changing behavior so that passing main-dex related information is a
compile-time error if the minimum api level is not below native multi-dex
support.

Bug:
Test: ./art/test/testrunner/run_build_test_target.py art-gtest
Change-Id: If662d8bd33da8cb576b4a6af0e40c949125c36c0