tools: Fix autopkgtest on Ubuntu
tools: Fix autopkgtest on Ubuntu

"useradd admin" failed because the admin group already exists. It's just
a legacy variant of "sudo" and not otherwise needed, so just nuke it for
the test.

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