info: report cgroup driver as "none" when running rootless
info: report cgroup driver as "none" when running rootless

Previously `docker info` had reported "cgroupfs" as the cgroup driver
but the driver wasn't actually used at all.

This PR reports "none" as the cgroup driver so as to avoid confusion.
e.g. kubeadm/kubelet will detect cgroupless-ness by checking this docker
info field. https://github.com/rootless-containers/usernetes/pull/97

Note that user still cannot specify `native.cgroupdriver=none` manually.

Signed-off-by: Akihiro Suda <10ddef0dea2a66ab193b07198faa879adcb213d8@hco.ntt.co.jp>

yongtang/docker,estesp/docker,paralin/docker,nawawi/docker,bearstech/moby,moul/docker,rremer/moby,rremer/moby,djs55/docker,moul/docker,crosbymichael/docker,justincormack/docker,nawawi/docker,jimjag/docker,trebonian/docker,pradipd/moby,AkihiroSuda/docker,jameszhan/docker,moul/docker,cpuguy83/docker,mahak/docker,jthelin/docker,cpuguy83/docker,yosifkit/docker,unclejack/docker,dims/docker,kolyshkin/moby,docker/docker,mahak/docker,thaJeztah/docker,ibuildthecloud/docker,mahak/docker,jimjag/docker,AkihiroSuda/docker,vdemeester/docker,Mokolea/docker,jvanz/docker,Ramzec/docker,crosbymichael/docker,nawawi/docker,Mokolea/docker,yosifkit/docker,Ramzec/docker,nawawi/docker,SvenDowideit/docker,ibuildthecloud/docker,gnailuy/docker,Mokolea/docker,yosifkit/docker,nalind/docker,gnailuy/docker,moby/moby,tmp6154/docker,dims/docker,crosbymichael/docker,konstruktoid/docker-1,flavio/docker,justincormack/docker,paralin/docker,Ramzec/docker,konstruktoid/docker-upstream,unclejack/docker,kojiromike/docker,moby/moby,yongtang/docker,pradipd/moby,flavio/docker,justincormack/docker,kojiromike/docker,AkihiroSuda/docker,cpuguy83/docker,ibuildthecloud/docker,kolyshkin/moby,bearstech/moby,konstruktoid/docker-upstream,kolyshkin/moby,jameszhan/docker,trebonian/docker,flavio/docker,djs55/docker,vdemeester/docker,flavio/docker,paralin/docker,paralin/docker,moby/moby,jimjag/docker,moul/docker,thaJeztah/docker,tmp6154/docker,jthelin/docker,SvenDowideit/docker,konstruktoid/docker-upstream,gnailuy/docker,jvanz/docker,jimjag/docker,nalind/docker,yongtang/docker,konstruktoid/docker-1,konstruktoid/docker-upstream,unclejack/docker,jvanz/docker,thaJeztah/docker,estesp/docker,ibuildthecloud/docker,konstruktoid/docker-1,nalind/docker,Mokolea/docker,docker/docker,docker/docker,jameszhan/docker,kojiromike/docker,Ramzec/docker,djs55/docker,bearstech/moby,ibuildthecloud/docker,trebonian/docker,thaJeztah/docker,estesp/docker,gnailuy/docker,AkihiroSuda/docker,cpuguy83/docker,trebonian/docker,dims/docker,yosifkit/docker,pradipd/moby,SvenDowideit/docker,bearstech/moby,moby/moby,rremer/moby,nalind/docker,mahak/docker,tmp6154/docker,vdemeester/docker