system: core: increase the polling time for remount_ro to 3600

eMMC4.5 introduces an addition of cache on the device.
We experienced long flush durations in some of the devices,
and therefore the adb reboot resets the target before the flush
completes.
Latest tests show that increasing it to 2400 wasn't enough thus
it was increased to 3600.

Conflicts:
	libcutils/android_reboot.c

Change-Id: Ifbe7af16aa1861d0d57c808b0240361c0317d5c5
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
Merge remote-tracking branch 'omni/android-4.4' into android-4.4