Use dex2oatd when available on debug builds

Enable use of dex2oatd for background dexopt service for eng and
userdebug builds.  This allows us to have more extensive checking
on dogfood devices.

Bug: 68025088
Test: runtest -x services/tests/servicetests/src/com/android/server/pm/dex/DexoptOptionsTests.java
Change-Id: I292ac7f355350edc8cf06f417740226ee6bac65d