Revert dexopt to /cache

Squash of the following commits:

Revert "libdex: Invert the default for dexopt-on-cache"

This reverts commit ff3989a9c0d2403eb3bbac3fa89a9ea001730725.

Partially revert "Unbreak building host modules"

This reverts commit 5531b23c1546fdf896db25f7412291bada6e723c.

Change-Id: I08b766fb96a700ecea6117d9d1a19a5fe0bd66fe

Revert "libdex: Skip the dexroot-on-cache stuff for user builds"

This reverts commit 3518b1a7dfc54c6db5078ac8f695dd9d6a60860d.

Revert "dvm: Bring back the ANDROID_DATA override"

This reverts commit 01ad455c149af55d34762c11ada603f61515d6bf.

Revert "DexOpt anything in /system on /cache"

This reverts commit 210ad4902c02500e55ec7e2e8b10f7079da442e2.

Change-Id: I7249239a66f107ad92499eb8bcd501ff8efbe300