Update run-tests script/dependencies to use -testdex jars.

run-tests run with --no-image need the dex files in the
bootclasspath to be available. The -testdex jars are guaranteed
unstripped, so use them instead.

This was always broken, but vmarko@ just added a test that
forces --no-image.

bug:24535627
Test: test-art-target

Change-Id: I391573cffd0749d814fd81517e99dfc8f0fd59d5