Try harder to support gtests with non-standard build config

One is able to set the location android builds to using the OUT_DIR
environment variable and android supports having this be a symlink.
Our gtests, however would fall over if you tried to run it using the
'm test-art-host-gtest' with anything other than OUT_DIR=out and out
as a real directory. If you broke this convention many tests would
fail because they are unable to find ANDROID_HOST_OUT.

This makes everything a little nicer by making common_art_test try to
figure out what ANDROID_HOST_OUT should be using the test binaries
location and commandline.

Test: export OUT_DIR=fast-out
      ln -s /some/other/path fast-out
      . build/envsetup.sh
      lunch aosp_walleye-userdebug
      m test-art-host-gtest

Change-Id: I67cdba43ef3050afe394cd03b14a43d309d020e2
2 files changed