logs: Don't show up messages when we stopped them
logs: Don't show up messages when we stopped them

There is race that when stop() is called, it stops existing processes but
right after it a new process is created and thus it keeps running forever.
Normally this would not be a problem, but with this weird
combination of JS + React it can happen that messages from this service
are shown in the UI.

mvollmer/cockpit,martinpitt/cockpit,cockpit-project/cockpit,mvollmer/cockpit,martinpitt/cockpit,garrett/cockpit,martinpitt/cockpit,garrett/cockpit,cockpit-project/cockpit,mvollmer/cockpit,garrett/cockpit,cockpit-project/cockpit,martinpitt/cockpit,mvollmer/cockpit,martinpitt/cockpit,mvollmer/cockpit,cockpit-project/cockpit,garrett/cockpit,garrett/cockpit,cockpit-project/cockpit