v1.12.0

Move pkg/util default storage functions from libpod to containers/storage
storage: make [l]chown errors clearer
Move lockfile_dawin.go to lockfile_otherunix.go to compile on freebsd
Add documentation about SELinux labeling
reexec: add CommandContext()
Drop our dependency on github.com/containers/image
imageStore: remove compatibity hacks for adding digests