Add new system APK locations.

Add /system/priv-app and /oem/app paths to system paths.  Also allow
rmdex on system apps, and quietly ignore when it was already removed.

Also relax logging when clearing code cache, since it's optional.

Bug: 17205122
Change-Id: I4fc4d0f63a3596937c4defbd64e1f8a1c563f02d