Fix image_space_test on Q+ target.

This is a follow-up after
    https://android-review.googlesource.com/958079
to make image_space_test pass when DEX2OATBOOTCLASSPATH is
set, i.e. on a Q+ device.

Test: image_space_test
Bug: 122937705
Change-Id: If84cde5e68ae42aed7d2a402817436c19ee6fc21
1 file changed