init: explicitly label all selinux files in rootfs

With system and vendor split, the files under them get labelled
differently as part of b/36527360. These files also include selinux
policy files if the policy is split. In order to consistently label
them, all sepolicy files on rootfs also are labelled with labels
matching to that of the ones in system and vendor. So, this now requires
init to explicitly label *all* selinux files in rootfs after
initializing selinux.

Test: Boot angler and ensure servicemananger continues to work (uses
      /{plat,nonplat}_service_contexts).
Test: Sideloaded OTA to angler to ensure recovery continues to work.
Test: Launch and load a website in Chrome.
Test: Launch camera and take picture, record video.

Change-Id: I4134eae80b5b51f381b549eb18e604cf271f9eb5
Signed-off-by: Sandeep Patil <sspatil@google.com>