Fixed the horrible OSX installation docs

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
cgroups: Update systemd to match fs backend

This updates systemd.Apply to match the fs backend by:
* Always join blockio controller (for stats)
* Support CpusetCpus
* Support MemorySwap

Also, it removes the generic UnitProperties in favour of a single
option to set the slice.

Docker-DCO-1.1-Signed-off-by: Alexander Larsson <alexl@redhat.com> (github: alexlarsson)
Merge pull request #5597 from jamtur01/docs-simplify-osx-install

Fixed the horrible OSX installation docs
Merge pull request #5354 from alexlarsson/cgroups-systemd-fixes

cgroups: Update systemd to match fs backend