test: Robustify check-packagekit
test: Robustify check-packagekit

After disabling rhsmd, also kill any running instance, so that it
doesn't trigger the "system is not subscribed" page.

Closes #13639

cockpit-project/cockpit,deryni/cockpit,garrett/cockpit,deryni/cockpit,cockpit-project/cockpit,cockpituous/cockpit,cockpit-project/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,garrett/cockpit,moraleslazaro/cockpit,deryni/cockpit,deryni/cockpit,mvollmer/cockpit,garrett/cockpit,moraleslazaro/cockpit,martinpitt/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,garrett/cockpit,mvollmer/cockpit,martinpitt/cockpit,deryni/cockpit,cockpituous/cockpit,martinpitt/cockpit,cockpituous/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,deryni/cockpit,deryni/cockpit,moraleslazaro/cockpit,cockpituous/cockpit,mvollmer/cockpit