selinux: Use a more reliable sentinel to flag /data labelling

/data/anr isn't present on all devices, /data/system is

Change-Id: Ifba71d073dc7b577911386cff316e8a19662cd0d
selinux: When adding userdata labels, do cache too

Change-Id: I0c1ff737629474135767be7cfe2bfbea0513fa9e
selinuxrelabel: Need to check in priv-app now

Change-Id: I67529c3b0f8baaac15fd475305eafd085feac112
Recheck /data for selinux labeling

This simply adds checks for selinux labels for
files under /data/misc/wifi which were not labeled
correctly for some devices

Change-Id: Iaacf6db792aaea1485502b424d639a1212c5841b
selinuxrelabel: Remove attempts to relabel /system

These are a no-op due to the additional block-device protection from
https://android.googlesource.com/platform/system/core/+/e18c0d508a6d8b4376c6f0b8c22600e5aca37f69
so get rid of them entirely. Any installing recovery (or equivalent
installation process) should handle the labeling of system components
on its own.

Change-Id: I14c50f08efa6f05b03fad4fbc404219cc504e1ff
TBD: Do we still want to label unlabeled files?