test: Check for sshd.service, not for dbus.service
test: Check for sshd.service, not for dbus.service

In latest Fedora 29, dbus.service got renamed to dbus-daemon.service. To
keep the test running between RHEL/CentOS 7 and Fedora 29, move to
dbus.service instead.

Closes #11045

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