Extend init and ueventd for SE Android.

Add SE Android support for init and ueventd.

init:
- Load policy at boot.
- Set the security context for service daemons and their sockets.
- New built-in commands: setcon, setenforce, restorecon, setsebool.
- New option for services: seclabel.

ueventd:
- Set the security context for device directories and nodes.

Change-Id: I98ed752cde503c94d99dfa5b5a47e3c33db16aac