Use dalvik.vm.background-dex2oat-* system properties for background

jobs.

This is done to align with ART Service behaviour (see
AddPerfConfigFlags in art/artd/artd.cc).

Test: atest run_dex2oat_test
Bug: 251903639
Change-Id: I68e20d32946c33b3c3d5d3a6bb15889a1209b1e1