Test all .art files in patchoat test

This augments the patchoat test to check all .art files produced by
dex2oat and patchoat, rather than just the main one -- boot.art.
For context, the test currently produces two .art files: boot.art and
boot-core-libart-hostdex.art.

Test: ./art/test/testrunner/run_build_test_target.py art-gtest-debug-gc
Test: make test-art-host-gtest-patchoat_test
Test: make test-art-target-gtest-patchoat_test
Bug: 66697305
Change-Id: I8a90e70811ac8b98a7c2de5bfe6a388ca884e259