restorecon_recursive("/sys") speed boot time

Currently, the restorecon_recursive("/sys") call in
init.c takes approx 2 seconds on hammerhead. This change
reduces the delay to 1.2 seconds.

1) Avoid double stat call when using nftw (time savings
of 0.3 seconds)
2) Avoid the repeated calls to is_selinux_enabled() (time
savings of 0.5 seconds)

Avoid calling lsetfilecon if the file is already properly
labeled. This doesn't speed up the restorecon on /sys,
but it should help when handling files on /data.

Change-Id: Icf344edc5bfc9520d3a0ebd9527a065d29832f87
Revert "restorecon_recursive("/sys") speed boot time"

this causes heavy random problems on selinux timings.

This reverts commit 4c6323ed9661508aaa576a15dc8a08ef3d624abe.

Change-Id: I31d89bb699233efd7b4fcaf9f7e207e3a0feea33
Add keystore to system group

 * Required in order to request firmware for hardware implementation

Change-Id: Ibd1ba79667d4489f0972b8fba587a8ba9c6083dd
fix up adb to prefer /sbin/sh if it exists

Change-Id: Ifa68efec387e6c12dc4bb2d0e764b8ecf96c0ad5