test: Mark debian-testing as having loopbacked docker storage
test: Mark debian-testing as having loopbacked docker storage

The current debian-testing image has a loopbacked docker storage
you can see this by doing:

    # systemctl start docker
    # losetup

Closes #7241
cockpit-project/cockpit,SotolitoLabs/cockpit,cockpit-project/cockpit,andreasn/cockpit,Scribery/cockpit,michalskrivanek/cockpit,harishanand95/cockpit,michalskrivanek/cockpit,garrett/cockpit,michalskrivanek/cockpit,larsu/cockpit,petervo/cockpit,cockpituous/cockpit,larsu/cockpit,stefwalter/cockpit,stefwalter/cockpit,xhad/cockpit,moraleslazaro/cockpit,petervo/cockpit,harishanand95/cockpit,martinpitt/cockpit,deryni/cockpit,harishanand95/cockpit,garrett/cockpit,larskarlitski/cockpit,martinpitt/cockpit,larskarlitski/cockpit,xhad/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,harishanand95/cockpit,larsu/cockpit,garrett/cockpit,mvollmer/cockpit,xhad/cockpit,xhad/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,mvollmer/cockpit,petervo/cockpit,larsu/cockpit,mareklibra/cockpit,cockpituous/cockpit,Scribery/cockpit,xhad/cockpit,deryni/cockpit,andreasn/cockpit,moraleslazaro/cockpit,garrett/cockpit,garrett/cockpit,petervo/cockpit,mareklibra/cockpit,Scribery/cockpit,larskarlitski/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,larskarlitski/cockpit,stefwalter/cockpit,andreasn/cockpit,stefwalter/cockpit,martinpitt/cockpit,harishanand95/cockpit,deryni/cockpit,harishanand95/cockpit,michalskrivanek/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,petervo/cockpit,mvollmer/cockpit,cockpituous/cockpit,cockpituous/cockpit,Scribery/cockpit,harishanand95/cockpit,larsu/cockpit,martinpitt/cockpit,SotolitoLabs/cockpit,michalskrivanek/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,andreasn/cockpit,Scribery/cockpit,mareklibra/cockpit,xhad/cockpit,SotolitoLabs/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,michalskrivanek/cockpit,larsu/cockpit,mvollmer/cockpit,andreasn/cockpit,cockpituous/cockpit,Scribery/cockpit,stefwalter/cockpit,cockpit-project/cockpit,andreasn/cockpit,deryni/cockpit,xhad/cockpit,deryni/cockpit,deryni/cockpit,cockpituous/cockpit,petervo/cockpit,michalskrivanek/cockpit,cockpit-project/cockpit,larskarlitski/cockpit,deryni/cockpit,andreasn/cockpit,larskarlitski/cockpit,cockpit-project/cockpit,petervo/cockpit,larskarlitski/cockpit,stefwalter/cockpit,Scribery/cockpit,mareklibra/cockpit