test: Don't run "docker pull".
test: Don't run "docker pull".

This is a source of unreliability.  The test machine images already
contain the "busybox" docker image.

Closes #2284
Reviewed-by: Stef Walter <8a7fbf0f15d3ad982af54ef28f5c117d2494b76c@redhat.com>

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