Add SELinux filesystem relabeling to init

Since not all recoveries out there will support the OTA packages'
own labeling, check at boot if the system needs labels (and
apply them)

Change-Id: I58767977b90a78a12efe7bd9d713654eadf47e7a

Conflicts:
	config/common.mk
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