Adjust forced dexopt in case of stripped APKs.

We cannot compile from scratch for strip APK. So
if getDexOptNeeded returns NotNeeded, pretend there was
a compiler filter change, in order to pick up the vdex file.

bug: 37558732
Test: "adb shell cmd package compile" of a stripped /system apk
Change-Id: I531010e01e44adfa300872c1739c49dab7292317