test: Fix stop_cockpit() to also stop the service
test: Fix stop_cockpit() to also stop the service

This is being used in check-connection. Just stopping the socket does
not prove anything, as cockpit.service is running while the login page
is being served. This corresponds to shutting down the ws container on
Atomic.

Closes #9235

mareklibra/cockpit,stefwalter/cockpit,stefwalter/cockpit,mvollmer/cockpit,cockpit-project/cockpit,mvollmer/cockpit,stefwalter/cockpit,andreasn/cockpit,deryni/cockpit,andreasn/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,garrett/cockpit,garrett/cockpit,cockpituous/cockpit,cockpituous/cockpit,mareklibra/cockpit,cockpit-project/cockpit,cockpituous/cockpit,mareklibra/cockpit,mareklibra/cockpit,cockpit-project/cockpit,deryni/cockpit,SotolitoLabs/cockpit,deryni/cockpit,cockpituous/cockpit,andreasn/cockpit,stefwalter/cockpit,stefwalter/cockpit,mvollmer/cockpit,moraleslazaro/cockpit,deryni/cockpit,martinpitt/cockpit,moraleslazaro/cockpit,cockpit-project/cockpit,andreasn/cockpit,moraleslazaro/cockpit,SotolitoLabs/cockpit,andreasn/cockpit,martinpitt/cockpit,SotolitoLabs/cockpit,martinpitt/cockpit,cockpituous/cockpit,mareklibra/cockpit,SotolitoLabs/cockpit,garrett/cockpit,andreasn/cockpit,moraleslazaro/cockpit,mvollmer/cockpit,SotolitoLabs/cockpit,stefwalter/cockpit,SotolitoLabs/cockpit,mareklibra/cockpit,moraleslazaro/cockpit,andreasn/cockpit,cockpituous/cockpit,garrett/cockpit,SotolitoLabs/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,martinpitt/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,deryni/cockpit,mareklibra/cockpit,deryni/cockpit,stefwalter/cockpit