Move the intermediate directory for ART boot images.

Free up the directory $(PRODUCT_OUT)/apex/com.android.art for the
release ART APEX. Without this we'll get conflicting install paths in
make.

Test: build/soong/soong_ui.bash --make-mode \
    TARGET_PRODUCT=sdk_x86_64 TARGET_BUILD_VARIANT=userdebug nothing
  with http://r.android.com/q/topic:release-apex-rename+author:mast
  present to rename the ART release APEX to com.android.art.
Test: Build & boot on CF
Test: apct/device_boot_test and asit/perf/boottime_test on
  blueline_jitzygote-userdebug
Test: avd/avd_boot_health_check on cf_x86_phone-userdebug_coverage_art
Bug: 169639321
Change-Id: I0b263d5922d438834e5c804e55f69a2a1421ab73
Merged-In: I0b263d5922d438834e5c804e55f69a2a1421ab73