dockerd-rootless.sh: support containerd v1.4 shim socket path convention
dockerd-rootless.sh: support containerd v1.4 shim socket path convention

The new shim socket path convention hardcodes `/run/containerd`:
https://github.com/containerd/containerd/pull/4343

`dockerd-rootless.sh` is updated to hide the rootful `/run/containerd`
from the mount namespace of the rootless dockerd.

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

trebonian/docker,kojiromike/docker,Mokolea/docker,docker/docker,cpuguy83/docker,dims/docker,Ramzec/docker,thaJeztah/docker,gnailuy/docker,flavio/docker,Ramzec/docker,ibuildthecloud/docker,yosifkit/docker,trebonian/docker,mahak/docker,nalind/docker,justincormack/docker,nawawi/docker,AkihiroSuda/docker,jameszhan/docker,thaJeztah/docker,konstruktoid/docker-upstream,moul/docker,cpuguy83/docker,kojiromike/docker,gnailuy/docker,jimjag/docker,flavio/docker,thaJeztah/docker,flavio/docker,bearstech/moby,moby/moby,jameszhan/docker,mahak/docker,nalind/docker,paralin/docker,moul/docker,moul/docker,yosifkit/docker,konstruktoid/docker-upstream,jimjag/docker,ibuildthecloud/docker,Ramzec/docker,bearstech/moby,moby/moby,cpuguy83/docker,moby/moby,nawawi/docker,trebonian/docker,djs55/docker,trebonian/docker,yosifkit/docker,yosifkit/docker,nalind/docker,justincormack/docker,AkihiroSuda/docker,moul/docker,Mokolea/docker,Mokolea/docker,docker/docker,vdemeester/docker,vdemeester/docker,nalind/docker,paralin/docker,nawawi/docker,flavio/docker,paralin/docker,bearstech/moby,nawawi/docker,Ramzec/docker,dims/docker,cpuguy83/docker,mahak/docker,vdemeester/docker,konstruktoid/docker-upstream,Mokolea/docker,kojiromike/docker,jthelin/docker,ibuildthecloud/docker,paralin/docker,docker/docker,jthelin/docker,justincormack/docker,djs55/docker,thaJeztah/docker,dims/docker,jimjag/docker,moby/moby,ibuildthecloud/docker,ibuildthecloud/docker,djs55/docker,AkihiroSuda/docker,konstruktoid/docker-upstream,jameszhan/docker,jimjag/docker,gnailuy/docker,bearstech/moby,AkihiroSuda/docker,mahak/docker,gnailuy/docker