dockerd-rootless.sh: use `command -v` instead of `which`
dockerd-rootless.sh: use `command -v` instead of `which`

`which` binary is often missing

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

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