Add tests for kernel selinux file api.

Add tests for kernel selinux files under /sys/fs/selinux.

Test: run vts -m VtsKernelSelinuxFileApi
Bug: 36902438
Bug: 36902877
Bug: 36902738
Change-Id: I1ed2ee7dc83cfb085f07257bab32f34451291935
8 files changed