test: Fix check-session for mobile
test: Fix check-session for mobile

Check for presence of `#nav-hosts-sel` to verify that the session is
still alive, as that is present in both desktop and mobile view.

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