Add more color and cgroupfs hierarchy verification to check-config.sh

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update contrib/check-config.sh to use zcat and grep if zgrep isn't available

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Update contrib/check-config.sh cgroupfs check to allow for something like '... cgroup rw,cpu' (looking at you, boot2docker)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)
Merge pull request #4968 from tianon/enhanced-check-config

Add more color and cgroupfs hierarchy verification to check-config.sh