test: Clean out build dir before building new rpms
test: Clean out build dir before building new rpms

This used to be done in machine.download_dir but
that was removed in 5abb3e6dd297111e291bd01fcab20eb8616c25da

Closes #4810
Reviewed-by: Stef Walter <8a7fbf0f15d3ad982af54ef28f5c117d2494b76c@redhat.com>

cockpit-project/cockpit,petervo/cockpit,mvollmer/cockpit,garrett/cockpit,Scribery/cockpit,sgallagher/cockpit,larsu/cockpit,larskarlitski/cockpit,arilivigni/cockpit,vanloswang/cockpit,garrett/cockpit,xhad/cockpit,petervo/cockpit,harishanand95/cockpit,SotolitoLabs/cockpit,dperpeet/cockpit,michalskrivanek/cockpit,harishanand95/cockpit,deryni/cockpit,arilivigni/cockpit,harishanand95/cockpit,stefwalter/cockpit,martinpitt/cockpit,deryni/cockpit,cockpit-project/cockpit,deryni/cockpit,mareklibra/cockpit,martinpitt/cockpit,andreasn/cockpit,larskarlitski/cockpit,dperpeet/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,larsu/cockpit,vanloswang/cockpit,petervo/cockpit,petervo/cockpit,michalskrivanek/cockpit,harishanand95/cockpit,stefwalter/cockpit,Scribery/cockpit,mareklibra/cockpit,cockpit-project/cockpit,arilivigni/cockpit,deryni/cockpit,cockpituous/cockpit,SotolitoLabs/cockpit,sgallagher/cockpit,dperpeet/cockpit,larskarlitski/cockpit,cockpituous/cockpit,larskarlitski/cockpit,xhad/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,cockpituous/cockpit,mareklibra/cockpit,vanloswang/cockpit,Scribery/cockpit,michalskrivanek/cockpit,andreasn/cockpit,moraleslazaro/cockpit,larskarlitski/cockpit,sgallagher/cockpit,deryni/cockpit,dperpeet/cockpit,stefwalter/cockpit,arilivigni/cockpit,cockpituous/cockpit,Scribery/cockpit,andreasn/cockpit,harishanand95/cockpit,martinpitt/cockpit,michalskrivanek/cockpit,vanloswang/cockpit,moraleslazaro/cockpit,garrett/cockpit,stefwalter/cockpit,martinpitt/cockpit,martinpitt/cockpit,arilivigni/cockpit,Scribery/cockpit,petervo/cockpit,SotolitoLabs/cockpit,xhad/cockpit,mareklibra/cockpit,dperpeet/cockpit,arilivigni/cockpit,moraleslazaro/cockpit,vanloswang/cockpit,michalskrivanek/cockpit,harishanand95/cockpit,Scribery/cockpit,moraleslazaro/cockpit,xhad/cockpit,cockpituous/cockpit,stefwalter/cockpit,larsu/cockpit,SotolitoLabs/cockpit,sgallagher/cockpit,sgallagher/cockpit,mvollmer/cockpit,michalskrivanek/cockpit,cockpit-project/cockpit,garrett/cockpit,andreasn/cockpit,larskarlitski/cockpit,petervo/cockpit,sgallagher/cockpit,harishanand95/cockpit,mvollmer/cockpit,petervo/cockpit,cockpit-project/cockpit,xhad/cockpit,Scribery/cockpit,vanloswang/cockpit,andreasn/cockpit,dperpeet/cockpit,moraleslazaro/cockpit,dperpeet/cockpit,xhad/cockpit,larsu/cockpit,deryni/cockpit,garrett/cockpit,mareklibra/cockpit,stefwalter/cockpit,michalskrivanek/cockpit,mvollmer/cockpit,xhad/cockpit,larsu/cockpit,mvollmer/cockpit,cockpituous/cockpit,larskarlitski/cockpit,andreasn/cockpit,mareklibra/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,larsu/cockpit,vanloswang/cockpit,sgallagher/cockpit,stefwalter/cockpit,deryni/cockpit,andreasn/cockpit,arilivigni/cockpit