Add label for kernel test files and executables

This required for kernel to do loopback mounts on filesystem
images created by the kernel system call tests in LTP.

Add a corresponding neverallow to stop all domains from accessing
the location at /data/local/tmp/ltp.

Bug: 73220071
Test: Boot sailfish successfully
Test: run vts-kernel -m VtsKernelLtp -t syscalls.fchown04

Change-Id: I73f5f14017e22971fc246a05751ba67be4653bca
Signed-off-by: Sandeep Patil <sspatil@google.com>