Modify init.rc and init.goldfish.rc for SE Android.

Set the security context for the init process.
Restore the security contexts of /cache and /data in case they were reset.
Specify the security context for services launched from the rootfs since
we cannot label their executables.
If on the emulator, set a policy boolean and restore the context of
/sys/qemu_trace to allow accesses not normally permitted on a device.

Change-Id: I166ffc267e8e0543732e7118eb0fd4b031efac3b
Signed-off-by: Stephen Smalley <sds@tycho.nsa.gov>