Chcon: use pwalk.Walk
Chcon: use pwalk.Walk

This gives me 1.5x speedup in comparison with filepath.Walk,
making the code as fast as chcon(3).

I am sure we can do better than that by eliminating os.Stat()
syscall and directory entries sorting done by filepath.Walk(),
but this means either another third-party package (such as
github.com/karrick/godirwalk) or rewriting the filepath.Walk()
from scratch. I'm still on the verge as whether we should do it.

Signed-off-by: Kir Kolyshkin <3a017b8ddb3f9cf3e4a59978b004111bdeb97f08@gmail.com>

opencontainers/selinux