test: Improve check-docker
test: Improve check-docker

Instead of changing ownership of the socket, we properly add "admin"
to the "docker" group.

Also, we restart docker.service instead of stopping it since stopping
it somehow causes the socket to have root:root ownership afterwards.

Closes #1489

arilivigni/cockpit,martinpitt/cockpit,SotolitoLabs/cockpit,Thermionix/cockpit,haiyangd/cockpit_view,deryni/cockpit,jscotka/cockpit,denysvitali/cockpit,cockpit-project/cockpit,martinpitt/cockpit,vanloswang/cockpit,haiyangd/cockpit_view,netzvieh/cockpit,vanloswang/cockpit,harishanand95/cockpit,matobet/cockpit,nmav/cockpit,sgallagher/cockpit,fridex/cockpit,moolitayer/cockpit,stefwalter/cockpit,Armstrong1992/cockpit,evol262/cockpit,cockpituous/cockpit,sub-mod/cockpit,sub-mod/cockpit,fridex/cockpit,xhad/cockpit,Scribery/cockpit,mvollmer/cockpit,mvollmer/cockpit,andreasn/cockpit,petervo/cockpit,evol262/cockpit,deryni/cockpit,denysvitali/cockpit,maxamillion/cockpit,moraleslazaro/cockpit,dperpeet/cockpit,zigitax/cockpit,fridex/cockpit,firebitsbr/cockpit,denysvitali/cockpit,dperpeet/cockpit,SotolitoLabs/cockpit,netzvieh/cockpit,Thermionix/cockpit,deryni/cockpit,dperpeet/cockpit,kkaempf/cockpit,larsu/cockpit,evol262/cockpit,mvollmer/cockpit,firebitsbr/cockpit,michalskrivanek/cockpit,matobet/cockpit,harishanand95/cockpit,vanloswang/cockpit,denysvitali/cockpit,stefwalter/cockpit,netzvieh/cockpit,mareklibra/cockpit,arilivigni/cockpit,garrett/cockpit,andreasn/cockpit,moraleslazaro/cockpit,andreasn/cockpit,martinpitt/cockpit,cockpit-project/cockpit,deryni/cockpit,larsu/cockpit,SotolitoLabs/cockpit,Scribery/cockpit,stefwalter/cockpit,maxamillion/cockpit,larskarlitski/cockpit,Scribery/cockpit,sub-mod/cockpit,moolitayer/cockpit,FireDrunk/cockpit,vbatts/cockpit,mareklibra/cockpit,mareklibra/cockpit,xhad/cockpit,dperpeet/cockpit,petervo/cockpit,fridex/cockpit,Armstrong1992/cockpit,larskarlitski/cockpit,deryni/cockpit,fridex/cockpit,fridex/cockpit,Thermionix/cockpit,haiyangd/cockpit_view,moraleslazaro/cockpit,dperpeet/cockpit,cockpit-project/cockpit,netzvieh/cockpit,netzvieh/cockpit,harishanand95/cockpit,nmav/cockpit,matobet/cockpit,firebitsbr/cockpit,SotolitoLabs/cockpit,arilivigni/cockpit,arilivigni/cockpit,Armstrong1992/cockpit,moolitayer/cockpit,FireDrunk/cockpit,mvollmer/cockpit,zigitax/cockpit,Scribery/cockpit,deryni/cockpit,darioajr/cockpit,harishanand95/cockpit,andreasn/cockpit,stefwalter/cockpit,darioajr/cockpit,moraleslazaro/cockpit,arilivigni/cockpit,haiyangd/cockpit_view,larskarlitski/cockpit,nmav/cockpit,arilivigni/cockpit,xhad/cockpit,SotolitoLabs/cockpit,michalskrivanek/cockpit,michalskrivanek/cockpit,vanloswang/cockpit,denysvitali/cockpit,garrett/cockpit,moolitayer/cockpit,Armstrong1992/cockpit,larskarlitski/cockpit,nmav/cockpit,zigitax/cockpit,jscotka/cockpit,FireDrunk/cockpit,andreasn/cockpit,moraleslazaro/cockpit,larskarlitski/cockpit,martinpitt/cockpit,kkaempf/cockpit,moraleslazaro/cockpit,vanloswang/cockpit,vbatts/cockpit,harishanand95/cockpit,firebitsbr/cockpit,garrett/cockpit,darioajr/cockpit,harishanand95/cockpit,petervo/cockpit,larskarlitski/cockpit,mareklibra/cockpit,evol262/cockpit,zigitax/cockpit,xhad/cockpit,vanloswang/cockpit,vbatts/cockpit,darioajr/cockpit,stefwalter/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,kkaempf/cockpit,jscotka/cockpit,cockpituous/cockpit,mareklibra/cockpit,firebitsbr/cockpit,haiyangd/cockpit_view,Thermionix/cockpit,moolitayer/cockpit,xhad/cockpit,sgallagher/cockpit,garrett/cockpit,sub-mod/cockpit,martinpitt/cockpit,kkaempf/cockpit,cockpit-project/cockpit,evol262/cockpit,maxamillion/cockpit,garrett/cockpit,maxamillion/cockpit,vbatts/cockpit,Armstrong1992/cockpit,SotolitoLabs/cockpit,petervo/cockpit,mareklibra/cockpit,sgallagher/cockpit,Thermionix/cockpit,dperpeet/cockpit,cockpituous/cockpit,dperpeet/cockpit,michalskrivanek/cockpit,matobet/cockpit,sgallagher/cockpit,FireDrunk/cockpit,xhad/cockpit,andreasn/cockpit,cockpit-project/cockpit,netzvieh/cockpit,petervo/cockpit,deryni/cockpit,kkaempf/cockpit,vbatts/cockpit,moraleslazaro/cockpit,larsu/cockpit,sgallagher/cockpit,cockpituous/cockpit,Thermionix/cockpit,Scribery/cockpit,jscotka/cockpit,cockpituous/cockpit,sgallagher/cockpit,larsu/cockpit,evol262/cockpit,FireDrunk/cockpit,michalskrivanek/cockpit,larsu/cockpit,vbatts/cockpit,xhad/cockpit,maxamillion/cockpit,mvollmer/cockpit,vanloswang/cockpit,larsu/cockpit,stefwalter/cockpit,petervo/cockpit,jscotka/cockpit,matobet/cockpit,stefwalter/cockpit,nmav/cockpit,zigitax/cockpit,michalskrivanek/cockpit,Scribery/cockpit,arilivigni/cockpit,matobet/cockpit,sub-mod/cockpit,harishanand95/cockpit,jscotka/cockpit,michalskrivanek/cockpit,sgallagher/cockpit,darioajr/cockpit,cockpituous/cockpit,petervo/cockpit,larskarlitski/cockpit,andreasn/cockpit,Scribery/cockpit